Performance information

• Photoluminescence properties of solid solutions of YNbO₄, GdNbO₄ and LuNbO₄
  Hayato Sato; Shohei Kodama; Ikuo Yanase; Hiroaki Takeda
  Journal of the Ceramic Society of Japan, 2025, [Reviewed]
  Ceramic Society of Japan, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.25015
  DOI ID：10.2109/jcersj2.25015, ISSN：1882-0743, eISSN：1348-6535
• Fine structural analysis of calcium–niobium–gallium garnet (CNGG) by single-crystal anomalous X-ray scattering　　　　　　　　　　　　　　　
  Ryo Yamane; Hiroaki Takeda; Takahiro Kuribayashi; Kazumasa Sugiyama; Tsuguo Fukuda
  Journal of Crystal Growth, First page：127947, Last page：127947, Oct. 2024, [Reviewed]
  Elsevier BV, Scientific journal
  DOI：https://doi.org/10.1016/j.jcrysgro.2024.127947
  DOI ID：10.1016/j.jcrysgro.2024.127947, ISSN：0022-0248
• Flux growth and evaluation of optical properties of Ce doped Li₂CaSiO₄ as a candidate for noble neutron scintillator　　　　　　　　　　　　　　　
  Shohei Kodama; Taiga Nishii; Miki Sodeno; Yusuke Urano; Shunsuke Kurosawa; Ikuo Yanase; Hiroaki Takeda
  Journal of the Ceramic Society of Japan, Volume：132, Number：7, First page：369, Last page：374, Jul. 2024, [Reviewed]
  This study focuses on the growth of transparent single crystals of Li2CaSiO4 (LCS) doped with Ce as neutron scintillator candidates. LCS is a light material with a high melting point and chemical stability; thus, LCS is applicable for use in high-flux neutron environments. However, the growth of transparent single crystals from the melt has been difficult owing to the phase transitions. In this study, the LiF/LiCl eutectic was used as a flux with a lower melting point and less decomposition than LiCl, and Ce was selected as the luminescent center. The phase diagram of the LiF/LiCl-LCS system was determined, and the conditions for crystal growth were optimized, consequently, transparent non-doped LCS and Ce:LCS crystals were successfully obtained. The alpha-ray-excited scintillation spectrum and scintillation decay time of Ce:LCS were measured in a feasibility study for neutron detection. The results showed that Ce:LCS has potential as a neutron scintillator, with a significantly fast decay time of 28.46 ns.
  Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.23214
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85197210970&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85197210970&origin=inward
  DOI ID：10.2109/jcersj2.23214, ISSN：1882-0743, eISSN：1348-6535, SCOPUS ID：85197210970
• Modification of photoluminescence wavelength and decay constant of Cr:Gd₃Ga₅O₁₂ substituted by Ca/Si cation pair
  Natsuki Shimoyama; Shohei Kodama; Karol Bartosiewicz; Chihaya Fujiwara; Ikuo Yanase; Hiroaki Takeda
  Journal of the Ceramic Society of Japan, Volume：132, Number：7, First page：364, Last page：368, Jul. 2024, [Reviewed]
  Ceramic Society of Japan, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.23216
  DOI ID：10.2109/jcersj2.23216, ISSN：1882-0743, eISSN：1348-6535
• Capture of CO₂ from ambient air by sodium manganate and CO₂ recovery at low temperatures　　　　　　　　　　　　　　　
  Ikuo Yanase; Hiroaki Nagashima; Teppei Okada; Shohei Kodama; Hiroaki Takeda
  Journal of Physics and Chemistry of Solids, Volume：187, Apr. 2024, [Reviewed]
  Sodium manganate (Na0.66MnO2, NMO) was synthesized by a liquid method using NaOH, Mn(NO3)2, and ethylenediaminetetraacetate. The absorption of CO2 from air by NMO was investigated at room temperature. The CO2 absorption by NMO was promoted at high relative humidity (RH) and accompanied by the formation of birnessite and sodium carbonate hydrate phases. NMO efficiently absorbed CO2 from air when the RH was greater than 60 % because adsorption of water vapor to NMO readily occurred above 60 % RH. Thus, NMO absorbed CO2 together with H2O adsorbed from the air. The regeneration of NMO, was accompanied by the release of CO2 from sodium carbonate hydrates and occurred at temperatures as low as 150 °C. This behavior was attributed the similar structural features of NMO and birnessite, which both incorporate layered structures composed of MnO6 octahedra.
  Scientific journal
  DOI：https://doi.org/10.1016/j.jpcs.2024.111866
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85182418063&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85182418063&origin=inward
  DOI ID：10.1016/j.jpcs.2024.111866, ISSN：0022-3697, SCOPUS ID：85182418063
• Effect of strontium substitution on growth and piezoelectric properties of calcium magnesium silicate Ca₂MgSi₂O₇ single crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Takumi Uehara; Genki Hirano; Shohei Kodama; Ikuo Yanase; Kazumasa Sugiyama
  Japanese Journal of Applied Physics, Volume：62, Number：SM, Nov. 2023, [Reviewed], [Lead]
  We report the effect of Sr substitution on the crystal growth and piezoelectric properties of calcium magnesium silicate Ca2MgSi2O7 (CMS) single crystals. Strontium-substituted CMS single crystals with a chemical composition of Ca1-x Srx MgSi2O7 (CSMS100x; x = 0.0 to 0.6) were grown using the conventional Czochralski method. CSMS100x crystals without impurity phases are obtained up to x = 0.5. Both crystallographic axis c and a increased with the Sr content x, and the crystallographic axis ratio a/c decreased. The piezoelectric d 36 constants obtained using CMS, CSMS30, and CSMS40 crystals decreased with an increase in the Sr content x. Based on these observations, a relationship between piezoelectric properties and crystal structure was found using data from 14 types of melilite-type crystals. It was found that d 36 increases with an increase in a/c.
  Scientific journal
  DOI：https://doi.org/10.35848/1347-4065/acf2a5
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85173570806&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85173570806&origin=inward
  DOI ID：10.35848/1347-4065/acf2a5, ISSN：0021-4922, eISSN：1347-4065, SCOPUS ID：85173570806
• Spark plasma sintering and ionic conductivity of Li_1.3Al_0.3Ti_1.7(PO₄)₃ fine particles synthesized by glass crystallization　　　　　　　　　　　　　　　
  Tatsuya Tezuka; Yuma Inagaki; Shohei Kodama; Hiroaki Takeda; Ikuo Yanase
  Powder Technology, Volume：429, First page：118870, Last page：118870, Nov. 2023, [Reviewed]
  Elsevier BV, English, Scientific journal
  DOI：https://doi.org/10.1016/j.powtec.2023.118870
  DOI ID：10.1016/j.powtec.2023.118870, ISSN：0032-5910
• Scanning time-resolved measurement of transient lattice strain on quartz oscillators resonating under alternating electric field
  Shinobu Aoyagi; Yuhei Kondo; Kazuhira Miwa; Hiroaki Takeda; Yusuke Hayakawa; Youichi Kaminaga; Hitoshi Osawa
  Japanese Journal of Applied Physics, Volume：62, Number：SM, First page：SM1028, Last page：SM1028, Sep. 2023, [Reviewed]
  Abstract
  
  Distributions of transient and local lattice strains on resonating AT-cut quartz oscillators were measured in situ by scanning time-resolved X-ray diffraction under an alternating electric field to reveal the effects of the crystal shape and electrode thickness on their piezoelectric vibration. The concentration of the lattice vibration amplitude and energy at the electrode center in a plano-convex type oscillator and enhancement of the lattice strain in a plano–plano type oscillator within the electrode area with increasing electrode thickness have been unambiguously demonstrated by the method without any surface modifications.
  IOP Publishing, Scientific journal
  DOI：https://doi.org/10.35848/1347-4065/acf475
  DOI ID：10.35848/1347-4065/acf475, ISSN：0021-4922, eISSN：1347-4065
• Cr-doped Al₂O₃–YAG binary and Al₂O₃–YAG–ZrO₂ ternary eutectic materials crystallized by the micro pulling down technique and their characterization
  J. Xu; Y. Guyot; A. Nehari; A. Pillonnet; G. Ledoux; H. Takeda; X. Xiaodong; K. Lebbou
  CrystEngComm, Volume：25, Number：34, First page：4834, Last page：4847, Jul. 2023, [Reviewed]
  Cr-doped Al₂O₃–YAG and Al₂O₃–YAG–ZrO₂ eutectic ceramics rods of 3 mm in diameter were solidified from the melt by a micro-pulling down (μ-PD) technique.
  Royal Society of Chemistry (RSC), Scientific journal
  DOI：https://doi.org/10.1039/d3ce00626c
  DOI ID：10.1039/d3ce00626c, eISSN：1466-8033
• Synthesis and photoluminescence properties of divalent rare-earth-doped Li₂CaSiO₄
  Shohei Kodama; Tomoki Saito; Ikuo Yanase; Hiroaki Takeda
  Journal of the Ceramic Society of Japan, Volume：131, Number：7, First page：258, Last page：262, Jul. 2023, [Reviewed]
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.22163
  DOI ID：10.2109/jcersj2.22163, ISSN：1882-0743, eISSN：1348-6535
• Synthesis and ionic conductivity of NASICON-type Li_1.4Al_0.4Ti_1.6(PO₄)₃ fine powder by a novel multi-step glass crystallization method　　　　　　　　　　　　　　　
  Tatsuya Tezuka; Kouki Kuribara; Shohei Kodama; Hiroaki Takeda; Ikuo Yanase
  Journal of Non-Crystalline Solids, Volume：590, First page：121675, Last page：121675, Aug. 2022, [Reviewed]
  Elsevier BV, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jnoncrysol.2022.121675
  DOI ID：10.1016/j.jnoncrysol.2022.121675, ISSN：0022-3093
• Position and electric field dependent local lattice strain detected by nanobeam x-ray diffraction on a relaxor ferroelectric single crystal
  Shinobu Aoyagi; Ayumi Aoyagi; Hiroaki Takeda; Hitoshi Osawa; Kazushi Sumitani; Yasuhiko Imai; Shigeru Kimura
  Physical Review B, Volume：105, Number：2, First page：024101, Jan. 2022, [Reviewed]
  American Physical Society (APS), English, Scientific journal
  DOI：https://doi.org/10.1103/physrevb.105.024101
  DOI ID：10.1103/physrevb.105.024101, ISSN：2469-9950, eISSN：2469-9969
• Growth and characterization of strontium-substituted La₃Ta_0.5Ga_5.5O₁₄ single crystals
  Hiroaki TAKEDA; Yudai SOBATA; Haruki USUI; Shohei KODAMA; Ikuo YANASE; Takuya HOSHINA; Takaaki TSURUMI; Kiyoshi SHIMAMURA
  Journal of the Ceramic Society of Japan, Volume：130, Number：1, First page：16, Last page：20, Jan. 2022, [Reviewed], [Lead, Corresponding]
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.21116
  DOI ID：10.2109/jcersj2.21116, ISSN：1882-0743, eISSN：1348-6535
• Effect of processing temperature on structural, optical and frequency dependent electrical responses of solid-state sintered bismuth sodium titanate　　　　　　　　　　　　　　　
  M.A. Zubair; F.A. Mozahid; H. Takeda; A.K.M.A. Hossain
  Materials Science and Engineering: B, Volume：274, First page：115474, Dec. 2021, [Reviewed]
  Elsevier BV, Scientific journal
  DOI：https://doi.org/10.1016/j.mseb.2021.115474
  DOI ID：10.1016/j.mseb.2021.115474, ISSN：0921-5107
• Na-ion conductivity of beta-NaFeO₂ synthesized from an EDTA chelate complex　　　　　　　　　　　　　　　
  Ikuo Yanase; Naoki Kuwada; Kouki Kuribara; Shohei Kodama; Hiroaki Takeda
  INORGANIC CHEMISTRY COMMUNICATIONS, Volume：134, First page：108913, Dec. 2021, [Reviewed]
  In this study, Na-ion conductivity of beta-NaFeO2 was improved by a low-temperature synthesis. A precursor Fecomplex containing ethylenediamine tetraacetate (EDTA) was prepared and then calcined at temperatures of 500-800 degrees C under flowing air (on heating) and Ar gas (on cooling). Single-phase beta-NaFeO2 powder was obtained at temperatures of 600-750 degrees C. The specific surface area of the beta-NaFeO2 powder increased as the calcination temperature decreased. The beta-NaFeO2 compact fabricated from the powder calcined at 600 degrees C had the largest density. Alternating current impedance analysis revealed that the resistivity of the grain boundaries in the compact decreased with increasing density, which improved the Na-ion conductivity of beta-NaFeO2. Thus, the Naion conductivity of beta-NaFeO2 was successfully improved by increasing its specific surface area.
  ELSEVIER, English, Scientific journal
  DOI：https://doi.org/10.1016/j.inoche.2021.108913
  DOI ID：10.1016/j.inoche.2021.108913, ISSN：1387-7003, eISSN：1879-0259, Web of Science ID：WOS:000710197900002
• Time-Resolved Nanobeam X-ray Diffraction of a Relaxor Ferroelectric Single Crystal under an Alternating Electric Field　　　　　　　　　　　　　　　
  Shinobu Aoyagi; Ayumi Aoyagi; Hiroaki Takeda; Hitoshi Osawa; Kazushi Sumitani; Yasuhiko Imai; Shigeru Kimura
  Crystals, Volume：11, First page：1419, Nov. 2021, [Reviewed]
  Scientific journal
  DOI：https://doi.org/10.3390/cryst11111419
  DOI ID：10.3390/cryst11111419, ORCID：103533945
• Novel application of Tb-substituted layered double hydroxides to capturing and photoluminescence detecting CO₂ gas at ambient temperature　　　　　　　　　　　　　　　
  Ikuo Yanase; Kouhei Hayashizaki; Masaki Kakiage; Hiroaki Takeda
  Inorganic Chemistry Communications, Volume：125, First page：108394, Last page：108394, Mar. 2021, [Reviewed], [Last]
  Elsevier BV, Scientific journal
  DOI：https://doi.org/10.1016/j.inoche.2020.108394
  DOI ID：10.1016/j.inoche.2020.108394, ISSN：1387-7003, eISSN：1879-0259, Web of Science ID：WOS:000620266700006
• Control of Thermophysical Properties of Langasite-Type La₃Ta_0.5Ga_5.5O₁₄ Crystals for Pressure Sensors　　　　　　　　　　　　　　　
  Haruki Usui; Makoto Tokuda; Kazumasa Sugiyama; Takuya Hoshina; Takaaki Tsurumi; Kheirreddine Lebbou; Ikuo Yanase; Hiroaki Takeda
  Crystals, Volume：10, Number：10, First page：936, Last page：936, Oct. 2020, [Reviewed], [Last, Corresponding]
  We present a possible method to reduce the anisotropy of the thermal stress generated on langasite-type La3Ta0.5Ga5.5O14 (LTG) piezoelectric crystals arising from the mismatch of the thermal expansion coefficients and Young’s moduli of the crystals and metals at high temperatures. To formulate this method, the thermal stresses of order-type langasite crystals, in which each cation site is occupied by one element only, were calculated and compared to each other. Our results suggest that the largest cation site affects the thermal stress. We attempted to replace La3+ in LTG by a larger ion and considered Sr2+. Single crystals of strontium-substituted LTG (Sr-LTG) were grown using the Czochralski method. The thermal stress along the crystallographic c-axis decreased but that perpendicular to the c-axis increased by strontium substitution into the LTG crystal. The anisotropic thermal stress was reduced effectively. The Sr-LTG single crystal is a superior candidate material for pressure sensors usable at high temperatures.
  MDPI AG, English, Scientific journal
  DOI：https://doi.org/10.3390/cryst10100936
  DOI ID：10.3390/cryst10100936, ISSN：2073-4352, eISSN：2073-4352, Web of Science ID：WOS:000584488200001
• Possibility of ferroelectric bismuth and nitrogen co-doped barium titanate　　　　　　　　　　　　　　　
  Takahiro YAMADA; Hiroaki TAKEDA; Takaaki TSURUMI; Takuya HOSHINA
  Journal of the Ceramic Society of Japan, Volume：128, Number：8, First page：486, Last page：491, Aug. 2020, [Reviewed]
  The possibility of bismuth (Bi) and nitrogen (N) co-doped barium titanate (BaTiO3) as a ferroelectric material was investigated by calculation and experiment. From first principles calculations, it was found that Bi and N co-doped BaTiO3 has a higher spontaneous polarization than undoped BaTiO3 since dopant Bi and N ions contribute to the enhancement of covalent interactions between cations and anions. Because it was revealed that the ferroelectricity of BaTiO3 can be improved by co-doping of Bi and N, we demonstrated the synthesis of (Ba,Bi)Ti(O,N)(3). Single phase oxynitride (Ba,Bi)Ti(O,N)(3) powder was fabricated by annealing (Ba,Bi)TiO3 in NH3 gas. The tetragonal distortion of (Ba,Bi)Ti(O,N)(3) was smaller than that of BaTiO3, which may be due to A-site and O-site vacancies in the perovskite lattice introduced during NH3 annealing. (C) 2020 The Ceramic Society of Japan. All rights reserved.
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.20020
  DOI ID：10.2109/jcersj2.20020, ISSN：1882-0743, eISSN：1348-6535, Web of Science ID：WOS:000557848300011
• Crystal growth and characterization of Li_xLa_(1−x)/3NbO₃ using Czochralski method　　　　　　　　　　　　　　　
  Shuya MINEGISHI; Takuya HOSHINA; Takaaki TSURUMI; Kheirreddine LEBBOU; Hiroaki TAKEDA
  Journal of the Ceramic Society of Japan, Volume：128, Number：8, First page：481, Last page：485, Aug. 2020, [Reviewed], [Last, Corresponding]
  Single crystals of LixLa(1-x)/3NbO3 were grown in air using Czochralski method from La-poor melt. The lithium-ion conductivity of the crystals was measured. The length and maximum diameter of the boule grown were 23 and 20 mm, respectively. The boule contained no inclusions but was covered with a very thin polycrystalline film of LaNbO4 and LiNbO3 in its upper region. The composition of the crystals grown was estimated to be x = 0.15 and the starting melt composition was x = 0.20. The ionic conductivity of the crystal was anisotropic with sigma([100]) = 2.8 x 10(-4)Scm(-1) and sigma([001]) = 9.7 x 10(-5) Scm(-1) at 306 K. The activation energy, E-a of these conductivities was almost the same in the range of 0.28-0.29 eV. Further, we discussed the anisotropic lithium-ion conductivity of the crystal. (C) 2020 The Ceramic Society of Japan. All rights reserved.
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.20026
  DOI ID：10.2109/jcersj2.20026, ISSN：1882-0743, eISSN：1348-6535, Web of Science ID：WOS:000557848300010
• Structure and electrical properties of Ba₃TaGa₃Si₂O₁₄ single crystals grown by Czochralski method　　　　　　　　　　　　　　　
  Haruki USUI; Hiraku KUSAKABE; Makoto TOKUDA; Kazumasa SUGIYAMA; Takuya HOSHINA; Takaaki TSURUMI; Hiroaki TAKEDA
  Journal of the Ceramic Society of Japan, Volume：128, Number：8, First page：441, Last page：446, Aug. 2020, [Reviewed], [Last, Corresponding]
  Ba3TaGa3Si2O14 (BTGS) bulk single crystals were grown by the Czochralski method. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data with a precision corresponding to an R index of 0.018. The crystal structure is isostructural to La3Ga5SiO14 which has the trigonal space group P321 and Z = 1, and the distribution of each cation is ordered in each site. Material constants and resistivity of the crystal were measured up to 550 degrees C. The results indicate that the BTGS crystal is a good candidate for piezoelectric applications in elevated temperatures. (C) 2020 The Ceramic Society of Japan. All rights reserved.
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.20016
  DOI ID：10.2109/jcersj2.20016, ISSN：1882-0743, eISSN：1348-6535, Web of Science ID：WOS:000557848300003
• Strontium-substituted calcium magnesium silicate single crystals for high-temperature piezoelectric applications　　　　　　　　　　　　　　　
  Hiroaki TAKEDA; Hiraku KUSAKABE; Haruki USUI; Takuya HOSHINA; Takaaki TSURUMI; Kheirreddine LEBBOU
  Journal of the Ceramic Society of Japan, Volume：128, Number：3, First page：130, Last page：134, Mar. 2020, [Reviewed], [Lead, Corresponding]
  We present a relationship between piezoelectric property and crystal structure in melilite-type crystals. Two independent piezoelectric constants, d(14) and d(36), increase and decrease with the polyhedral distortion, respectively. Based on this knowledge, single crystals made of strontium-substituted calcium magnesium silicate Ca2MgSi2O7 (CMS) have been submitted to the Czochralski method, which made them grown. The CMS crystal has a high d(36); however, its transition temperature is around 85 degrees C. Therefore, the strontium substitution is conducted to decrease this phase transition temperature. A single crystal of strontium substituted CMS, with nominal chemical composition Ca1.7Sr0.3MgSi2O7 (CSMS30), shows no phase transition when temperature rises from room to melting temperature. Its piezoelectric d'(31) constant is 2.1 pC/N and its compressive strength is 830MPa on crystal substrate with (ZXt)45 degrees cut. The CSMS30 single crystal is a superior candidate material for pressure sensors at high operating temperatures. (C) 2020 The Ceramic Society of Japan. All rights reserved.
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.19193
  DOI ID：10.2109/jcersj2.19193, ISSN：1882-0743, eISSN：1348-6535, Web of Science ID：WOS:000516765300004
• Terahertz dielectric response of nano-grained barium titanate ceramics measured by far-infrared spectroscopic ellipsometry　　　　　　　　　　　　　　　
  YuHsun Liao; Shuhei Takezawa; Hiroaki Takeda; Takaaki Tsurumi; Takuya Hoshina
  Japanese Journal of Applied Physics, Volume：58, Number：SL, First page：SLLA07, Nov. 2019, [Reviewed]
  The effect of grain size on ionic polarization of pure BaTiO3 ceramics was investigated. BaTiO3 ceramics with various grain sizes ranging from 434 nm to 1.85 mu m were fabricated by a two-step sintering method. The samples indicated a similar trend in the relationship between grain size and permittivity at low frequencies as other studies, with 803 nm grains having the highest permittivity among the samples. In the THz region, the central, Slater, Last, and Axe modes were observed using a far-infrared ellipsometer. The vibration frequencies of the Slater, Last and Axe modes were 115, 179, and 490 cm(-1), respectively, and did not change with decreasing grain size. In contrast, the central mode was shown to be influenced by the grain size. The grain size dependence of the central mode contribution was discussed based on the effect of the formation of 90 degrees domain configurations and the grain boundary stress. (C) 2019 The Japan Society of Applied Physics
  IOP Publishing, English, Scientific journal
  DOI：https://doi.org/10.7567/1347-4065/ab38d2
  DOI ID：10.7567/1347-4065/ab38d2, ISSN：0021-4922, eISSN：1347-4065, Web of Science ID：WOS:000497974800007
• Doping effect of Nb on ionic polarization of SrTiO₃　　　　　　　　　　　　　　　
  Nishiyama Junji; Kanehara Kazuki; Takeda Hiroaki; Tsurumi Takaaki; Hoshina Takuya
  Journal of the Ceramic Society of Japan, Volume：127, Number：6, First page：357, Last page：361, Jun. 2019, [Reviewed]
  THz dielectric spectra of Nb-doped SrTiO3 single crystals were measured using the far-infrared spectroscopic ellipsometer to understand the doping effect of Nb on ionic polarization. The frequency of the Slater transverse optical (TO) mode increased with the doping amount of Nb, meaning the decrease in the ionic polarization by Nb doping. From the change in the Slater TO mode frequency, it was estimated that the ionic polarizability of 1% Nb-doped SrTiO3 was 10.4% lower than that of undoped SrTiO3. This result suggested that the intrinsic permittivity of Nb-doped SrTiO3 is lower than that of that of undoped SrTiO3. First principles calculations revealed that the Nb 4d-orbitals contributes to the covalency between B-site cations and O ions, however, the covalency is suppressed due to the electron carrier doping. The doped electrons causes the decrease in the long-range Coulomb force and the increase in short-range elastic force, and therefore the ionic polarizability is decreased by Nb doping. (C)2019 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.19031
  DOI ID：10.2109/jcersj2.19031, ISSN：1882-0743, eISSN：1348-6535, Web of Science ID：WOS:000485680600005
• Electroacoustical constants and Rayleigh surface acoustic wave propagation characteristics of calcium aluminate silicate Ca₂Al₂SiO₇ single crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Kyohei Akimoto; Takuto Oshima; Kenta Takizawa; Jun Kondoh; Akihiro Matsutani; Takuya Hoshina; Takaaki Tsurumi
  Japanese Journal of Applied Physics, Volume：57, Number：11, First page：11UD01, Nov. 2018, [Reviewed], [Lead, Corresponding]
  Electroacoustical constants (epsilon(T)(ij), s(ij)(E), and d(ij)) of calcium aluminate silicate Ca2Al2SiO7 piezoelectric single crystals, which have the tetragonal structure with the point group 42m, were evaluated. The normalized first-order temperature coefficients of all the constants were determined between -30 and 120 degrees C at 10 kHz frequency, e.g., for epsilon(T)(11) and epsilon(T)(33) were 69.3 and 87.6, and for d(14) and d(36) were -338.4 and 552.4 ppm/degrees C, respectively. The Rayleigh surface acoustic wave (SAW) velocities for the fundamental X- and Z-cuts of the crystals were theoretically calculated. The results were supported by the SAW velocities measured for the Z-cut of the crystal, proving the accuracy of the electroacoustic constants determined in this study. (C) 2018 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.57.11UD01
  DOI ID：10.7567/JJAP.57.11UD01, ISSN：0021-4922, eISSN：1347-4065, Web of Science ID：WOS:000450231800015
• Time-resolved structure analysis of piezoelectric crystals by X-ray diffraction under alternating el
  Aoyagi Shinobu; Osawa Hitoshi; Sugimoto Kunihisa; Nakahira Yuki; Moriyoshi Chikako; Kuroiwa Yoshihiro; Takeda Hiroaki; Tsurumi Takaaki
  Japanese Journal of Applied Physics, Volume：57, Number：11, First page：11UB06, Nov. 2018, [Reviewed]
  IOP Publishing, Scientific journal
  DOI：https://doi.org/10.7567/jjap.57.11ub06
  DOI ID：10.7567/jjap.57.11ub06, ISSN：0021-4922, eISSN：1347-4065
• Grain size effect on piezoelectric properties of BaTiO₃ ceramics　　　　　　　　　　　　　　　
  Hoshina Takuya; Hatta Saki; Takeda Hiroaki; Tsurumi Takaaki
  Japanese Journal of Applied Physics, Volume：57, Number：9, First page：0902BB, Sep. 2018, [Reviewed]
  We demonstrated the grain size effect on piezoelectric properties of pure BaTiO3 ceramics. BaTiO3 ceramics with various grain sizes were prepared by conventional and two-step sintering methods. The piezoelectric strain constant d(33) increased with decreasing grain size when the grain size was more than 1.2 mu m, whereas it decreased when the grain size was below 1.2 mu m. The maximum d(33) was 460 pC/N, which is approximately three times larger than that of coarse BaTiO3 ceramics. The increase in d(33) was well explained by the domain-wall contribution, while the decrease in d(33) was understood as the grain boundary effect On the other hand, the piezoelectric voltage constant g(33) increased with decreasing grain size down to 0.6 mu m. The piezoelectric constants d(33) and g(33), and the mechanical quality factor Q(m) can be controlled by the grain size of BaTi(O3 )ceramics. (C) 2018 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.57.0902BB
  DOI ID：10.7567/JJAP.57.0902BB, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804431, Web of Science ID：WOS:000437483500001
• Structure of russellite (Bi₂WO₆): origin of ferroelectricity and the effect of the stereoactive lone electron pair on the structure　　　　　　　　　　　　　　　
  Hiroki Okudera; Yuka Sakai; Kentaro Yamagata; Hiroaki Takeda
  Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, Volume：74, Number：3, First page：295, Last page：303, Jun. 2018, [Reviewed], [Last]
  The structure of the low-temperature polar (orthorhombic) phase of russellite (Bi2WO6) was examined on artificial specimens with precise single-crystal X-ray diffraction experiments. The final atomic arrangement thus obtained was identical to that reported by Knight [Miner. Mag. (1992), 56, 399–409] with powder neutron diffraction. The residual density attributable to a stereochemically-active lone pair of electrons of bismuth was prominent at approximately the centre of a larger cap of BiO8 square antiprisms, that is on the line from the Bi sites to an adjacent WO4 2− slab along the b-axis direction. Quite uneven Bi—O distances and the formation of a vacant coordination hemisphere (within 3 Å) should, therefore, be ascribed to the strong demand of bismuth to form shorter Bi—O bonds to use up its electrostatic charge within its coordination environment. The shift of bismuth along −c propagates via the correlated shift of the W site and these cooperative shifts cause ferroelectricity in the compound. This propagation was easily effected by the intrusion of molecules such as acetone into the structure.
  Wiley-Blackwell, English, Scientific journal
  DOI：https://doi.org/10.1107/S2052520618006133
  DOI ID：10.1107/S2052520618006133, ISSN：2052-5206, ORCID：47804433, SCOPUS ID：85048500840, Web of Science ID：WOS:000434798000005
• Growth and characterization of Ca_2-xAe_xAl₂SiO₇ (Ae = Sr, Ba) piezoelectric single crystals　　　　　　　　　　　　　　　
  Takuto Oshima; Takuya Hoshina; Takaaki Tsurumi; Kheirreddine Lebbou; Hiroaki Takeda
  Journal of the Ceramic Society of Japan, Volume：126, Number：5, First page：300, Last page：305, May 2018, [Reviewed], [Last, Corresponding]
  We report the effects of Sr or Ba substitution on the crystal growth and electrical and mechanical properties of Ca2Al2SiO7 (CAS) piezoelectric single crystals, which are suitable for use in high-temperature pressure sensors. Ba was scarcely incorporated in the crystal lattice of CAS. Strontium-substituted CAS single crystal with a nominal chemical composition Ca0.75Sr1.25Al2SiO7 (CSAS125) was grown by the Czochralski method. Although the piezoelectric modulus d¤31 of CSAS125 is a bit lower than that of the CAS crystal, the rupture strength of the (XYt)45° rotation cut substrate of CSAS125 crystal was 170 MPa, which was 1.2 times higher than that of CAS crystal. By considering the rupture strength and the apparent piezoelectric d31 coefficient calculated for the crystal rotation cut of CAS crystal, the CSAS125 crystal substrate with a rotation cut of (XYt)25° was found to indicate a rupture strength of 220 MPa and a piezoelectric d¤31 coefficient of approximately 2 pC/N.
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.17263
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85046375329&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85046375329&origin=inward
  DOI ID：10.2109/jcersj2.17263, ISSN：1348-6535, eISSN：1348-6535, ORCID：47804432, SCOPUS ID：85046375329, Web of Science ID：WOS:000431293500008
• Effect of oxygen vacancies on intrinsic dielectric permittivity of strontium titanate ceramics　　　　　　　　　　　　　　　
  Takuya Hoshina; Ryuichi Sase; Junji Nishiyama; Hiroaki Takeda; Takaaki Tsurumi
  Journal of the Ceramic Society of Japan, Volume：126, Number：5, First page：263, Last page：268, May 2018, [Reviewed]
  We prepared oxygen-deficient strontium titanate ceramics and measured the THz dielectric spectra to discuss the effect of oxygen vacancies on the intrinsic dielectric permittivity. In the presence of oxygen vacancies, the lattice volume of strontium titanate increased. First-principles calculation revealed that the expansion of the lattice originated from repulsion between the oxygen vacancies and cations, causing a decrease in the covalency of the TiO bonding. THz dielectric measurement using a far-infrared spectroscopic ellipsometer made it clear that the Slater-type phonon mode hardened and then the intrinsic permittivity of strontium titanate decreased in the presence of oxygen vacancies.
  Ceramic Society of Japan, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.17250
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85046361765&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85046361765&origin=inward
  DOI ID：10.2109/jcersj2.17250, ISSN：1348-6535, eISSN：1348-6535, ORCID：47804430, SCOPUS ID：85046361765, Web of Science ID：WOS:000431293500002
• Transparent semiconducting SrTiO₃ crystal fabricated by heating treatment with gaseous ammonia and CeO₂ powder　　　　　　　　　　　　　　　
  Yuka Morimoto; Junji Nishiyama; Hiroaki Takeda; Takaaki Tsurumi; Takuya Hoshina
  Scientific Reports, Volume：8, First page：5031, Mar. 2018, [Reviewed]
  A transparent semiconducting SrTiO3 single crystal with a resistivity of the order of 103 Ω·cm was fabricated by heating a SrTiO3 single crystal with gaseous ammonia and CeO2 powder. Conductive atomic force microscope (C-AFM) measurement revealed that micro-sized voids were formed and the high conductivity was exhibited only at around the voids. It is considered that the micro-sized voids were caused by the concentrated SrO planar defects, and TiO2-terminated structure with oxygen vacancies contributed to the two-dimensional conduction. In the heating process, the CeO2 powder acted as an oxygen source, and radicals such as NH2 and NH were generated by the reaction of oxygen and ammonia. The radicals may have contributed to the formation of three-dimensional network of the conductive paths consisting of SrO planar defects without the reduction of the bulk components. The electrons were localized on the TiO2-terminated structure, and the volume content of the conductive paths was small compared to the insulating bulk component. Therefore, the crystal was optically transparent and semiconducting.
  Nature Publishing Group, English, Scientific journal
  DOI：https://doi.org/10.1038/s41598-018-23019-9
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85044400513&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=85044400513&origin=inward
  DOI ID：10.1038/s41598-018-23019-9, ISSN：2045-2322, eISSN：2045-2322, ORCID：47804434, PubMed ID：29568047, SCOPUS ID：85044400513, Web of Science ID：WOS:000428032800003
• Optical and structural characterization of ZnSe thin film fabricated by thermal vapour deposition technique　　　　　　　　　　　　　　　
  Mohammed Tareque Chowdhury; Md. Abdullah Zubair; Hiroaki Takeda; Kazi Md. Amjad Hussain; Md. Fakhrul Islam
  AIMS Materials Science, Volume：4, Number：5, First page：1095, Last page：1121, Oct. 2017, [Reviewed]
  Zinc-selenide thin film was prepared on a soda-lime glass substrate by thermal vapor deposition technique. The X-ray diffraction data confirmed the cubic zincblende structure with a preferred orientation along (111) plane. Different models such as Debye-Scherrer, Size-Strain plot, Williamson-Hall, uniform stress deformation model and uniform deformation energy density model and the so called approximation model were adopted to analyse the XRD data. Detailed microstructural parameters such as crystallite size, strain, stress, isotropic energy density, dislocation denstiy were reported and discussed in comparison with scanning electron microscopy data. The transmission spectra was obtained by UV-Vis-NIR spectrometer in the range of 250-2500 nm at room temperature. Important optical constantssuch as refractive index and dielectric constant was estimated using Swanepoel's envelope method. The same method was used to check the thin film thickness which was found to be ~ 374.9 nm and this thickness was further confirmed by Scanning Electron Microscopy (368.3 ± 19.1 nm). The optical band gap was estimated to be 2.64 eV. The dispersion of refractive index was discussed interms of empirical Cauchy dispersion relation and the dispersion was further analysed by Wemple-DiDomenico Single oscillator model which provide physically meaningful parameters such as static refractive index, oscillator energy and dispersion energy. Both the structural and optical data not only complemented each other but also implied that good quality Zinc-selenide thin film could be deposited on ordinary glass substrates.
  AIMS Press, English, Scientific journal
  DOI：https://doi.org/10.3934/matersci.2017.5.1095
  DOI ID：10.3934/matersci.2017.5.1095, ISSN：2372-0468, ORCID：47804439, SCOPUS ID：85037068782, Web of Science ID：WOS:000416071600005
• Elution of lead from lead zirconate titanate ceramics to acid rain　　　　　　　　　　　　　　　
  Takaaki Tsurumi; Shuhei Takezawa; Takuya Hoshina; Hiroaki Takeda
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：56, Number：10, First page：10PD01, Oct. 2017, [Reviewed]
  The amount of lead that eluted from lead zirconate titanate (PZT) ceramics to artificial acid rain was evaluated. Four kinds of PZT ceramics, namely, pure PZT at MPB composition, CuO-added PZT, PZT with 10 mol% substitution of Ba for Pb, and CuO-added PZT with 10 mol% substitution of Ba for Pb, were used as samples of the elution test. These PZT ceramics of 8mm(2) and 1.1-1.2 mm thickness were suspended in 300 ml of H2SO4 solution of pH 4.0. The concentration of lead eluted from PZT was in the range from 0.2 to 0.8 ppm. It was found that both liquid phase formation by the addition of CuO and the substitution of Ba for Pb were effective to reduce the amount of lead that eluted. By fitting the leaching out curve with a classical equation, a master curve assuming no sampling effect was obtained. The lead concentration evaluated from the amount of lead that eluted from a commercial PZT plate to H2SO4 solution of pH 5.3 was almost the same as the limit in city water. It is concluded that PZT is not harmful to health and the environment and the amount of lead that eluted from PZT can be controlled by modifying PZT composition. (C) 2017 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.56.10PD01
  DOI ID：10.7567/JJAP.56.10PD01, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804436, Web of Science ID：WOS:000413800800024
• Effect of atomic vacancies on ionic polarization of nonstoichiometric strontium titanate ceramics　　　　　　　　　　　　　　　
  Ryuichi Sase; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：56, Number：10, First page：10PB11, Oct. 2017, [Reviewed]
  We prepared nonstoichiometric strontium titanate with different Sr/Ti atomic ratios and measured the THz dielectric spectra to discuss the effect of atomic vacancies on the ionic polarization. In the presence of atomic vacancies in strontium titanate, the lattice volume increased and the dielectric permittivity decreased. The expansion of the lattice volume originated from repulsion between oxygen vacancies and cations or between cation vacancies and O ions, causing the reduction in the covalency of the Ti-O bond. In addition, THz dielectric spectra and first-principles calculation revealed that the reduction of permittivity is mainly explained by the hardening of the Slater-type phonon mode. In the presence of oxygen- and titanium-vacancies, the repulsion of the Ti-O bond increased, and then the ionic polarization due to the Slater mode decreased. (C) 2017 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.56.10PB11
  DOI ID：10.7567/JJAP.56.10PB11, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804435, Web of Science ID：WOS:000413800800013
• Formation of sodium bismuth titanatebarium titanate during solid-state synthesis　　　　　　　　　　　　　　　
  Dong Hou; Elena Aksel; Chris M. Fancher; Tedi-Marie Usher; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi; Jacob L. Jones
  JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Volume：100, Number：4, First page：1330, Last page：1338, Apr. 2017, [Reviewed]
  Phase formation of sodium bismuth titanate (Na0.5Bi0.5TiO3 or NBT) and its solid solution with barium titanate (BaTiO3 or BT) during the calcination process is studied using in situ high-temperature diffraction. The reactant powders were mixed and heated to 1000 degrees C, while X-ray diffraction patterns were recorded continuously. Phase evolutions from starting materials to final perovskite products are observed, and different transient phases are identified. The formation mechanism of NBT and NBT-xBT perovskite structures is discussed, and a reaction sequence is suggested based on the observations. The in situ study leads to a new processing approach, which is the use of nano-TiO2, and gives insights to the particle size effect for solid-state synthesis products. It was found that the use of nano-TiO2 as reactant powder accelerates the synthesis process, decreases the formation of transient phases, and helps to obtain phase-pure products using a lower thermal budget.
  WILEY, English, Scientific journal
  DOI：https://doi.org/10.1111/jace.14631
  DOI ID：10.1111/jace.14631, ISSN：0002-7820, eISSN：1551-2916, ORCID：47804437, Web of Science ID：WOS:000399610800014
• Growth and characterization of strontium-substituted Ca₂Al₂SiO₇ piezoelectric single crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Kyohei Yoshida; Hiroki Okudera; Kheirreddine Lebbou; Takuya Hoshina; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：125, Number：1, First page：23, Last page：26, Jan. 2017, [Reviewed], [Lead, Corresponding]
  We report the effect of Sr substitution on the structural, electrical, and mechanical properties of Ca2Al2SiO7 (CAS) piezoelectric single crystals for high-temperature pressure sensors. Single crystals of Sr-substituted CAS (Sr-CAS) with a nominal chemical composition of CaSrAl2SiO7 were grown by using the Czochralski technique. The single-crystal X-ray structure analysis revealed that Sr atoms were placed in the Ca decahedral sites, which decreased the polyhedral distortion slightly. The piezoelectric modulus d'(31) and electrical resistivity of Sr-CAS measured at 23 degrees C were slightly lower than those of CAS, but still sufficient for the satisfactory performance of the produced sensors. The rupture strength of the Sr-CAS crystal was 230 MPa, 1.2 times higher than that of a CAS crystal. The obtained results suggest that Sr-CAS crystals can be candidate materials for high-temperature pressure sensors. (C) 2017 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.16206
  DOI ID：10.2109/jcersj2.16206, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804438, Web of Science ID：WOS:000392432500005
• Electro-optic effect and photoelastic effect of feroelectric relaxors　　　　　　　　　　　　　　　
  Kotaro Takeda; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：55, Number：10, Oct. 2016, [Reviewed]
  To understand the origin of the electro-optic effect (EO-effect) of ferroelectric relaxors, the relationships among the quadratic EO-coefficient, photoelastic coefficient, and electron density were elucidated. The quadratic EO-coefficient is given by the product of the photoelastic and electrostrictive coefficients. Materials consisting of heavy elements normally exhibit high refractive indices and large photoelastic effects, indicating that the photoelastic coefficient increases with electron density of materials. The photoelastic coefficient was calculated as a function of the electron density of materials. The equations derived in this study were experimentally confirmed using lanthanum-added lead-zirconate-titanate (PLZT) transparent ceramics. It was found that the origin of the EO-effect in ferroelectric relaxors was the photoelastic effect coupled with electric-field- induced strain via the piezoelectric and electrostrictive effects. (C) 2016 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.55.10TB05
  DOI ID：10.7567/JJAP.55.10TB05, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804440, Web of Science ID：WOS:000391101200026
• Wideband dielectric spectroscopy of (Sr_0.7Bi_0.2)TiO₃ ceramics and its microscopic mechanism of polarization　　　　　　　　　　　　　　　
  Motoharu Sakurai; Kazuki Kanehara; Hiroaki Takeda; Takaaki Tsurumi; Takuya Hoshina
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：124, Number：6, First page：664, Last page：667, Jun. 2016, [Reviewed]
  (Sr0.7Bi0.2)TiO3 ceramics were fabricated by a solid state reaction, and a wideband dielectric spectrum was measured for understanding the microscopic polarization mechanism of (Sr0.7Bi0.2)TiO3 ceramics. It was revealed that the dielectric permittivity of (Sr0.7Bi0.2)TiO3 ceramics at 25 degrees C was determined by dipole polarization as well as ionic polarization, whereas the permittivity of SrTiO3 is mainly determined only by ionic polarization. The temperature dependence of permittivity suggested that (Sr0.7Bi0.2)TiO3 ceramics belongs to ferroelectric relaxor, in which off-center Bi3+ ions contribute to the formation of polar nanoregions (PNRs). The origin of the dipole polarization is considered the dipole fluctuations of PNRs. On the other hand, the ionic polarization of (Sr0.7Bi0.2)TiO3 ceramics was suppressed by an influence of Sr-site vacancy, compared to that of SrTiO3. High permittivity of (Sr0.7Bi0.2)TiO3 ceramics is mainly due to the dipole polarization associated with dipole fluctuation of PNRs. (C) 2016 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.16023
  DOI ID：10.2109/jcersj2.16023, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804441, Web of Science ID：WOS:000379611300010
• Effects of aluminum substitution on the structure and electric properties of langasite family crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Jun-ichi Yamaura; Takashi Nishida; Takuya Hoshina; Takaaki Tsurumi
  CRYSTAL RESEARCH AND TECHNOLOGY, Volume：50, Number：12, First page：944, Last page：949, Dec. 2015, [Reviewed], [Lead, Corresponding]
  The effects of aluminum substitution on the structure and electric properties of langasite (La3Ga5SiO14) family crystals are reported. The maximum Al content x of La3Ga5-xAlxSiO14 (LGAS), La3Nb0.5Ga5.5-xAlxO14 (LNGA), and La3Ta0.5Ga5.5-xAlxO14 (LTGA) crystals grown by the conventional Czochralski technique are x = 0.9, 0.2, and 0.5, respectively. Single-crystal X-ray structural analysis reveals that Al atoms are distributed in all cation sites except for the decahedral one occupied by La, rather than favoring the smallest tetrahedral sites. The electrical properties of the Al-substituted crystals were also compared with those of pure ones. Al substitution was found to affect the piezoelectric constant d(14), but not d(11). The LGAS and LTGA crystals exhibit higher electric resistivity rho as a result of Al substitution. Among the Al-substituted and pure crystals, the LTGA crystal featured the lowest temperature dependence of d(11) and highest rho, making it the most suitable of the group for high-temperature piezoelectric applications.
  WILEY-V C H VERLAG GMBH, English, Scientific journal
  DOI：https://doi.org/10.1002/crat.201500261
  DOI ID：10.1002/crat.201500261, ISSN：0232-1300, eISSN：1521-4079, ORCID：47804444, Web of Science ID：WOS:000368276700005
• Fabrication and characterization of dielectric strontium titanium oxynitride single crystal　　　　　　　　　　　　　　　
  Takuya Hoshina; Akira Sahashi; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：54, Number：10, Oct. 2015, [Reviewed]
  In this paper, we show a fabrication method and the dielectric properties of strontium titanium oxynitride (SrTiO3:N) single crystals. Oxynitride single crystals were prepared by annealing SrTiO3 single crystals in gaseous ammonia. SrTiO3:N was assumed to have the chemical composition SrTiO3-3xN2x, which contained oxygen vacancies. To reduce the number of oxygen vacancies, SrTiO3 crystals co-doped with nitrogen and niobium (SrTiO3:N,Nb) were fabricated. The semiconducting Nb-doped SrTiO3 crystals changed to dielectric N,Nb-codoped SrTiO3 crystals with a resistivity of 6 x 10(12)Omega.cm with annealing in gaseous ammonia. XPS measurement indicated that niobium doping was effective for increasing the amount of dopant nitrogen. The dielectric permittivity increased with the amount of dopant nitrogen, indicating the effectivity of nitrogen doping for increasing the dielectric permittivity of perovskite oxides. (C) 2015 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.54.10NB05
  DOI ID：10.7567/JJAP.54.10NB05, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804445, Web of Science ID：WOS:000362286000023
• Development of microscopic measurement system for electro-optic effect　　　　　　　　　　　　　　　
  Ryuta Yamamoto; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：123, First page：929, Last page：932, Sep. 2015, [Reviewed]
  This paper reports a microscopic electro-optic (EO) effect measurement system that is based on the Senarmont method and enables measurement of the EO coefficients (Kerr coefficients) of submillimeter-sized crystalline materials. In this study, an estimation of the electric field applied to the crystalline sample was performed with a finite-element method because the parallel plate electrodes were required to be on the same side of the sample surface. Reproducible values of the EO coefficients of submillimeter-sized (Pb,La)(Zr,Ti)O-3 transparent ceramics were obtained only if this estimation was taken into account. This system will effectively increase the speed of searches for new EO materials. (C) 2015 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.123.929
  DOI ID：10.2109/jcersj2.123.929, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804443, Web of Science ID：WOS:000362504400038
• Terahertz permittivity of rutile TiO₂ single crystal measured by anisotropic far-infrared ellipsometry　　　　　　　　　　　　　　　
  Kazuki Kanehara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：123, First page：303, Last page：306, May 2015, [Reviewed]
  Rutile structured TiO2 has very high dielectric permittivities in non-ferroelectric materials. To understand the reason why rutile TiO2 has high ionic polarizabilities, it is essential to analyze accurate dielectric spectra of rutile TiO2 in the THz region. In this study, the complex permittivity of rutile TiO2 single crystal in the range 30-700 cm(-1) (0.90-21 THz) was directly measured using the anisotropic far-infrared spectroscopic ellipsometer. The three E-u modes and one A(2u) mode, which are all infrared-active phonon modes in rutile TiO2, were observed. Moreover, the resonance frequencies of the phonon modes approximately were coincident with a calculation result of first-principles and the analysis data by a harmonic oscillator model. From the examination of the dielectric response, it was found that Eu(1) mode, which indicates the oscillation of Ti ions against O ions in the same phase, was dominant contributor to the static permittivity for a-axis. On the other hand, the high permittivity for c-axis was due to "soft" A(2u) mode. (C) 2015 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.123.303
  DOI ID：10.2109/jcersj2.123.303, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804446, Web of Science ID：WOS:000353912500001
• Design and fabrication of acoustic matching layer for lead-free ultrasonic flowmeter　　　　　　　　　　　　　　　
  Mei Hotate; Daichi Yoshidome; Takahiro Kojima; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：123, First page：317, Last page：321, May 2015, [Reviewed]
  We designed and fabricated acoustic matching layers made of a BaTiO3/epoxy 0-3 composite material for a lead-free ultrasonic flowmeter. Specific acoustic impedance of fabricated 0-3 composite was controlled by changing volume fraction of BaTiO3 fine particles. When the volume fraction of BaTiO3 fine particles was 40 vol % or less, sufficiently uniform 0-3 composite materials and various specific acoustic impedances of 2.6-6.9 x 10(6) kg/m(2)s were obtained. For improving an accuracy of a lead-free ultrasonic transducer with (K,Na) NbO3-based ceramics, a pair of acoustic matching layers with a specific acoustic impedance of 6.35 x 10(6) kg/m(2)s and a thickness of 0.260 mm were fabricated. By using the fabricated acoustic matching layers in a lead-free ultrasonic flowmeter, the amplitude of output voltage was improved by 35% compared to that using commercialized matching layers. Even in comparison with the commercialized ultrasonic flowmeter with PZT-based materials, the amplitude of output voltage with the fabricated composite matching layers was 83.1%. The lead-free ultrasonic flowmeter with the fabricated composite matching layer had high accuracy of a flow rate error of 3.5% or less. From above results, the effectiveness of the optimized composite matching layers was verified. (C) 2015 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.123.317
  DOI ID：10.2109/jcersj2.123.317, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804442, Web of Science ID：WOS:000353912500004
• Terahertz dielectric response of single-domain BaTiO₃ measured by far-infrared spectroscopic ellipsometry　　　　　　　　　　　　　　　
  Takuya Hoshina; Kazuki Kanehara; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：53, Number：9, First page：09PD03, Sep. 2014, [Reviewed]
  The complex dielectric permittivity of single-domain BaTiO3 in the region of 30-700 cm(-1) (0.90-21 THz) was directly measured using a far-infrared spectroscopic ellipsometer. The dielectric responses of the Slater, Last, Axe, and O-4 torsional modes, which are all infrared-active phonon modes in BaTiO3 were clearly observed. The resonance frequencies of the phonon modes estimated in this study were in agreement with the previous data estimated by analysis of reflection spectra using a harmonic oscillator model. These results indicate that the far-infrared ellipsometric technique is effective for analyzing the phonon modes of BaTiO3 single crystals. Additionally, we examine the dielectric response and the damping of the soft mode with respect to the order-disorder model. (C) 2014 The Japan-Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.53.09PD03
  DOI ID：10.7567/JJAP.53.09PD03, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804454, Web of Science ID：WOS:000343068600035
• Measurement of ionic polarization of SrTiO₃ single crystal by far-infrared spectroscopic ellipsometry　　　　　　　　　　　　　　　
  Kazuki Kanehara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  APPLIED PHYSICS LETTERS, Volume：105, Number：4, First page：042901, Jul. 2014, [Reviewed]
  We developed a far-infrared spectroscopic ellipsometer for measuring the complex permittivity of high-permittivity materials in the terahertz (THz) region and demonstrated the dielectric function of SrTiO3 single crystal at 0.75-21 THz. The responses of the Slater, Last, and O-6 displacive modes, which are all optical phonon modes of SrTiO3 at room temperature, were clearly observed. The complex permittivity measured by the ellipsometer agreed with the permittivity simulated by a damped harmonic oscillator model. The far-infrared spectroscopic ellipsometry is useful to analyze the phonon modes of high-permittivity materials, which enable us to understand the contribution of the ionic polarizations to the low-frequency permittivity. (C) 2014 AIP Publishing LLC.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.4891767
  DOI ID：10.1063/1.4891767, ISSN：0003-6951, eISSN：1077-3118, ORCID：47804452, Web of Science ID：WOS:000341152600059
• Fabrication of ferroelectric silicate KNbSi₂O₇ single crystal　　　　　　　　　　　　　　　
  Akira Sahashi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：122, First page：389, Last page：392, Jun. 2014, [Reviewed]
  ABSi(2)O(7) is a new ferroelectric material group of which ferroelectricity has been discovered recently. In this study, we focused on potassium niobate silicate (KNbSi2O7), which comprises displacement-type ferroelectric substance KNbO3 and high-covalence substance SiO2 in the structure. KNbSi2O7 single crystals with a size of 10 x 10 x 1mm(3) were fabricated by the process of glass crystallization, re-melting, and slow-cooling. The polarization-electric field (P-E) curve of the KNbSi2O7 crystal was evaluated and KNbSi2O7 evidently showed ferroelectricity in the direction of c axis. The value of the spontaneous polarization was estimated to 0.11 mu C/cm(2). The dielectric permittivity was approximately 15 for both a and c axes at 1 MHz, and this material was found to be a ferroelectric material with low dielectric permittivity. (C) 2014 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.122.389
  DOI ID：10.2109/jcersj2.122.389, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804450, Web of Science ID：WOS:000342065200006
• Effects of Ca substitution on room temperature resistivity of donor-doped barium titanate based PTCR ceramics　　　　　　　　　　　　　　　
  Kohei Matsuura; Takuya Hoshina; Hiroaki Takeda; Yukio Sakabe; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：122, First page：402, Last page：405, Jun. 2014, [Reviewed], [Corresponding]
  Barium titanate based semiconducting ceramics were synthesized using Ca2+ and La3+ as dopants, TiO2, SiO2 and MnO as sintering aids, and various firing process. The Ca2+ contained ceramics without impurity phases, sintered in reducing atmosphere and subsequent annealing in air, showed both the PTCR (Positive Temperature Coefficient of Resistivity) behavior and low room temperature resistivity rho(RT) 2.2 Omega cm. Based on knowledge of ionization energy and bond disassociation energy, it was cleared that Ca substitution plays an important role in lowering the rho(RT) value in the ceramics. (C) 2014 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.122.402
  DOI ID：10.2109/jcersj2.122.402, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804449, Web of Science ID：WOS:000342065200009
• Phase transition of Bi$_2$WO$_6$ below 300 K　　　　　　　　　　　　　　　
  Yoneda, Yasuhiro; Takeda, Hiroaki; Tsurumi, Takaaki
  JPS Conference Proceedings (Internet), Volume：1, First page：012103\_1, Last page：012103\_4, Mar. 2014, [Reviewed]
  Bi$_2$WO$_6$ is the simplest member of the Aurivillius family of (Bi$_2$O$_2$)(A$_{m-1}$B$_m$O$_{3m+1}$) with one oxygen octahedron sandwiched between two Bi$_2$O$_2$ layers (m=1). We report the high-energy synchrotron X-ray diffraction study of ferroelectric Bi$_2$WO$_6$ at low temperatures, and a new phase transition was found around 200 K. The mechanism of this phase transition was examined by atomic pair-distribution function (PDF) method.
  English
  DOI：https://doi.org/10.7566/JPSCP.1.012103
  DOI ID：10.7566/JPSCP.1.012103
• Origin of Semiconducting Behavior of CaO Added BaTiO₃-(Bi_1/2Na_1/2)TiO₃ Ceramics　　　　　　　　　　　　　　　
  Hitomi Akutsu; Mohammad A. Zubair; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：582, First page：92, Last page：95, Jan. 2014, [Reviewed]
  An effect of addition of CaO on electrical resistivity in BaTiO3-(Bi1/2Na1/2)TiO3 (BT-BNT) solid solution ceramics was investigated. Three kinds of CaO adding processes were applied. Extra CaO additive against stoichiometric composition is effective to give semiconductive property into the BT-BNT ceramics. However, the ceramics with CaO-inclusive composition such as Ba-0.9(B0.5Na0.15Ca0.35)(0.1)TiO3 had a high resistivity. From chemical composition analysis and structure analysis, it was concluded that Ca2+ dominantly substituted for Na+ in the A site of perovskite-type ABO(3) structure and then that residual Bi3+ acts a donor.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.582.92
  DOI ID：10.4028/www.scientific.net/KEM.582.92, ISSN：1013-9826, ORCID：47804453, Web of Science ID：WOS:000336235300022
• Improvement of insulation reliability of BaTiO₃-based ceramics using mixed conductive electrode　　　　　　　　　　　　　　　
  Daichi Yoshidome; Takuya Hoshina; Hiroaki Takeda; Yukio Sakabe; Takaaki Tsurumi
  Key Engineering Materials, Volume：582, First page：44, Last page：47, Jan. 2014, [Reviewed]
  The insulation degradation of BaTiO3-based ceramics under direct-current field is caused by the migration of oxygen vacancies. To improve the reliability of BaTiO3-based ceramic capacitors, conventional approaches are focusing on dielectrics, mainly working on suppressing the total amount of oxygen vacancies towards the cathode. In this study, we newly focus NOT on the dielectrics but on the electrodes, and tried to improve the reliability of BaTiO3-based ceramics by suppressing the segregation of migrated oxygen vacancies. La0.8Sr0.2MnO3 (LSM) is a mixed ionic-electronic conductor that generates oxide ions from gas-phase oxygen. We expected that LSM would compensate for migrated oxygen vacancies when using it as the cathode of a BaTiO3-based ceramic capacitor. The results of our highly-accelerated life tests indicate that the reliability of BaTiO3-based ceramics improved when LSM porous ceramics was used only as the cathode, (NOT the anode).
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.582.44
  DOI ID：10.4028/www.scientific.net/KEM.582.44, ISSN：1013-9826, ORCID：47804451, Web of Science ID：WOS:000336235300011
• Domain Contribution to Elastic Nonlinearity in Pb(Zr, Ti)O₃-based Piezoelectric Ceramics　　　　　　　　　　　　　　　
  Manabu Hagiwara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：582, First page：3, Last page：6, Jan. 2014, [Reviewed]
  In order to clarify the origin of the elastic nonlinearity in piezoelectric ceramics, the effect of Mn substitution into Pb(Zr,Ti)O-3-based ceramics on the nonlinear elastic stiffness was investigated by analyzing the transient response after burst excitation. The real part of 3rd-order elastic stiffness drastically decreased with increasing Mn content. It was also found that the appearance of the elastic nonlinearity enhanced the mechanical loss. From the results, the irreversible domain wall motion overcoming the potential barrier due to defect complexes was considered as a possible origin of the elastic nonlinearity.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.582.3
  DOI ID：10.4028/www.scientific.net/KEM.582.3, ISSN：1013-9826, ORCID：47804448, Web of Science ID：WOS:000336235300001
• Characterization of Cu₂O Thin Film grown by Molecular Beam Epitaxy　　　　　　　　　　　　　　　
  Takumi Oshima; Masaya Nohara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：582, First page：157, Last page：160, Jan. 2014, [Reviewed]
  We report the growth of Cu2O thin films on glass and MgO(100) substrates by molecular beam epitaxy. Crystal orientation of Cu2O thin films on glass substrate were changed from (100) to (111) with increasing the deposition rate. The Cu2O thin films were epitaxially grown on MgO(100) substrate with an orientation relationship of Cu2O(110) parallel to MgO(100). The film quality and electrical properties of Cu2O thin films were changed with deposition rate. The slow deposition rate resulted in high conductivity and mobility, as well as good crystallinity and orientation.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.582.157
  DOI ID：10.4028/www.scientific.net/KEM.582.157, ISSN：1013-9826, ORCID：47804447, Web of Science ID：WOS:000336235300037
• Bulk response and grain boundary microelectrical activity of high T_C BaTiO₃-(Bi_1/2K_1/2)TiO₃-based positive temperature coefficient of resistance ceramics　　　　　　　　　　　　　　　
  Zubair Mohammad A; Takeda Hiroaki; Leach Colin; Freer Robert; Hoshina Takuya; Tsurumi Takaaki
  Journal of Materials Research, Volume：28, Number：21, First page：2946, Last page：2959, Nov. 2013, [Reviewed], [Corresponding]
  Lead-free positive temperature coefficient of resistance (PTC) thermistors were synthesized from (1 - x/100)BaTiO3-(x/100)(Bi1/2K1/2)TiO3-based solid solutions, using a conventional mixed-oxide fabrication route, and sintered in N-2 followed by air annealing. A maximum T-C of 205 degrees C was achieved for x = 20. An increase in x from 0 to 20 decreased the grain size by more than 92% and increased room temperature resistivity (rho(RT)) by 7 orders of magnitude. For x <= 10, PTC ratio (rho(max)/rho(min)) approximate to 10(4.5) and temperature coefficient of resistivity (alpha) > 10.3%/degrees C were achieved using Mn and Al2O3:SiO2:TiO2 (AST) additions. For x > 10, rho(max)/rho(min) > 10(3) and alpha > 8%/degrees C were only obtained in samples sintered in N-2 without subsequent air annealing. Complex impedance analysis revealed three relaxation processes, attributed to a semiconducting grain core, a PTC active grain boundary interface, and a grain boundary insulating layer. Local electrical activity was investigated by hot-stage conductive mode microscopy. The existence of symmetrical grain boundary electron beam-induced current and beta-conductivity contrast at the grain boundaries, consistent with the presence of an electron trapping two-dimensional grain boundary plane, compensated by positive space charge layers and a low conductivity vacancy-rich layer, was revealed for the first time within this system.
  CAMBRIDGE UNIV PRESS, English, Scientific journal
  DOI：https://doi.org/10.1557/jmr.2013.282
  DOI ID：10.1557/jmr.2013.282, ISSN：0884-2914, eISSN：2044-5326, ORCID：47804456, Web of Science ID：WOS:000326936700003
• Synthesis of Lead-Free Air-Sintered BaTiO₃-(Bi_1/2Na_1/2)TiO₃-Based Positive-Temperature-Coefficient of Resistance Ceramics by Ca Addition and the Defect Chemistry of Semiconductivity　　　　　　　　　　　　　　　
  Mohammad A. Zubair; Hiroaki Takeda; Takuya Hoshina; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：52, Number：9, First page：09KG01, Sep. 2013, [Reviewed], [Corresponding]
  Lead-free n-type [Ba-0.9(Ba1/2Na1/2)(0.1)]TiO3-based positive-temperature-coefficient of resistance (PTC) ceramics with T-C > 158 degrees C were successfully synthesized by addition of 2-4 mol% CaO through a mixed oxide fabrication route and adopting an atmospheric sintering condition. All ceramics exhibited single phase BaTiO3 structure with 64.21(1) angstrom(3) cell volume. A drop in room-temperature resistivity (rho(RT)) by 7-8 orders magnitude in presence of the CaO was attributed to residual Ba2+ site Bi3+ acting as donor defect owing to filling up of vacancies introduced by the preferential evaporation of Na+ over Bi3+ by Ca2+. Increases in rho(RT) and the maximum PTC resistivity (rho(max)) from 0.316 to 2.11 k Omega.cm and from 0.085 to 2.94 M Omega.cm, respectively, with 2 to 4 mol% CaO addition were attributed to the gradual incorporation of Ca2+ into both Ba2+ and Ti4+ sites, which oxidized the electron hopping centers (Ti3+) through the generation of holes. The optimum CaO content (3.5 mol %), sintering time (2 h) and temperature (1160 degrees C) were established to achieve [Ba-0.9(Ba1/2Na1/2)(0.1)]TiO3-based semiconducting PTC ceramics by adopting an atmospheric sintering environment. (C) 2013 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.52.09KG01
  DOI ID：10.7567/JJAP.52.09KG01, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804466, Web of Science ID：WOS:000324890800053
• Growth and Characterization of Ca₂Al₂SiO₇ Piezoelectric Single Crystals for High-Temperature Sensor Applications　　　　　　　　　　　　　　　
  Manabu Hagiwara; Hiroaki Noguchi; Takuya Hoshina; Hiroaki Takeda; Shinobu Fujihara; Nobuhiro Kodama; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：52, Number：9, First page：09KD03, Sep. 2013, [Reviewed], [Corresponding]
  The electrical properties of a piezoelectric single crystal of calcium aluminate silicate Ca2Al2SiO7 (CAS) were studied at elevated temperatures and its applicability to high-temperature pressure sensors was investigated. The CAS bulk single crystal was grown by the Czochralski method. The piezoelectric d(14) and d(36) constants were respectively evaluated as 6.04 and 4.04 pC/N by the resonance and antiresonance method. The temperature dependence of the piezoelectric constant was investigated at temperatures up to 500 degrees C. The electrical resistivity at 800 degrees C was on the order of 10(8) Omega.cm along both the crystallographic a-and c-axes. The measurement of direct piezoelectric response at 700 degrees C demonstrated that the CAS crystal could detect a pseudo-combustion pressure change of an automobile engine. Our observations suggest that CAS crystals are superior candidates for sensing pressure at high temperatures. (C) 2013 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.52.09KD03
  DOI ID：10.7567/JJAP.52.09KD03, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804460, Web of Science ID：WOS:000324890800026
• Grain Size Effect on Dielectric Properties of Ba_0.92Ca_0.08TiO₃ Ceramics　　　　　　　　　　　　　　　
  Takuya Hoshina; Tsutomu Furuta; Takahiro Yamazaki; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：52, Number：9, First page：09KC05, Sep. 2013, [Reviewed]
  We demonstrated the grain size effect on the dielectric properties of Ba0.92Ca0.08TiO3 ceramics. Fine-grained Ba0.92Ca0.08TiO3 ceramics with micrometer-and nanometer-sized grains were fabricated by the two-step sintering method and aerosol deposition method, respectively. The permittivity of Ba0.92Ca0.08TiO3 ceramics increased with decreasing grain size when the grain size was more than 400 nm, whereas it decreased when the grain size was below 400 nm. The permittivity of Ba0.92Ca0.08TiO3 ceramics with micrometer-sized grains was lower than that of BaTiO3 ceramics. This was caused by the hardening of the soft mode and the decrease in the 90 degrees domain-wall contribution by Ca substitution. Moreover, the grain size that gave the maximum permittivity for Ba0.92Ca0.08TiO3 ceramics was lower than that for BaTiO3 ceramics. This result suggested that the Ba0.92Ca0.08TiO3 was less sensitive to the grain size effect than BaTiO3 ceramics. These features in the grain size dependence of permittivity were explained by the tetragonal structure stability of Ba0.92Ca0.08TiO3. (C) 2013 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.52.09KC05
  DOI ID：10.7567/JJAP.52.09KC05, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804459, Web of Science ID：WOS:000324890800022
• Design, simulation, and fabrication of longitudinal electro-optically tuned transparent-comb-electrode photonic crystals　　　　　　　　　　　　　　　
  Jong-Min Oh; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：121, First page：659, Last page：663, Aug. 2013, [Reviewed], [Corresponding]
  We designed advanced transparent-comb-electrode photonic crystals (TCE PCs) to use the longitudinal electro-optic (LEO) effect, so they are composed of Al-doped ZnO (AZO) layers, which serve as internal/external electrodes, and centered (Pb,La)(Zr,Ti)O-3 (PLZT) layers, which serve as EO material. The simulated transmittance spectra of a multilayer interference (MLI) model revealed the conditions in the AZO and PLZT film thicknesses and the AZO/PLZT period number for a narrow photonic band gap (PBG). The TCE PCs consisted of four periods of AZO/PLZT, and it was fabricated by RF magnetron sputtering through metal mask patterning. Finally, a refractive index change induced by the LEO effect of the PLZT layers was accomplished by applying the voltage dependence of transmittance spectra that were well fitted with a revised (MLI) model considering light absorption and scattering. The PCs exhibit large refractive index changes of 1.3 x 10(-2) and 2.9 x 10(-2) at DC voltages of 4 and 8 V, respectively. The corresponding PBG shifts were 3.9 and 8.5 nm, implying high a PBG tunability of similar to 1 nm/V. (C) 2013 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.121.659
  DOI ID：10.2109/jcersj2.121.659, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804458, Web of Science ID：WOS:000330212700019
• Relation between electro-optic effect and dielectric permittivity of Ba_0.5Sr_0.5TiO₃ thin films　　　　　　　　　　　　　　　
  Kotaro Takeda; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：566, First page：20, Last page：24, Jul. 2013, [Reviewed]
  The relation between the dielectric tunability and the electro-optic (EO) effect of barium strontium titanate (Ba0.5Sr0.5TiO3) thin film was discussed. The tunability of dielectric permittivity calculated from the complex admittance with planer electrodes reached to 53.1%, and the tunability of birefringence by EO effect was 0.6%. The birefringence change from EO effect was much lower than the tunability of dielectric permittivity. The materials with high tunability do not always exhibit high EO effect. This is concluded to arise due to the ionic mass in the EO materials.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.566.20
  DOI ID：10.4028/www.scientific.net/KEM.566.20, ISSN：1013-9826, ORCID：47804465, Web of Science ID：WOS:000324451300005
• Polarization mechanism of fine-grained BaTiO₃ ceramics at high temperature region　　　　　　　　　　　　　　　
  Takahiro Yamazaki; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：566, First page：12, Last page：15, Jul. 2013, [Reviewed]
  Pure Barium titanate (BaTiO3) ceramics with grain sizes of 0.6, 1.5, and 18 μm on average were prepared by using a two-step sintering method. The wideband dielectric spectra in the range from kHz to THz were measured at 25 and 150 °C to understand the polarization mechanism of fine-grained BaTiO3 ceramics. It was revealed that the dipole and ionic polarizations decreased with decreasing grain size at 25 and 150 °C when the grain size was smaller than 1 μm. These mechanisms were interpreted as a grain boundary effect. © (2013) Trans Tech Publications.
  English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.566.12
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84883491784&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84883491784&origin=inward
  DOI ID：10.4028/www.scientific.net/KEM.566.12, ISSN：1013-9826, eISSN：1662-9795, ORCID：47804464, SCOPUS ID：84883491784, Web of Science ID：WOS:000324451300003
• Influence of atmosphere on resistivity of aluminum substituted La₃Ta_0.5Ga_5.5O₁₄ single crystals during growth and annealing process　　　　　　　　　　　　　　　
  Hiroaki Noguchi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：566, First page：81, Last page：84, Jul. 2013, [Reviewed], [Corresponding]
  Aluminum substituted La3Ta0.5Ga5.5O 14 (LTGA) single crystals were grown via a floating zone (FZ) method in N2 or O2 gas flows. Also, LTGA single crystals that were grown using the Czochralski method were annealed in N2 or O 2 gas flows. The resistivity of these crystals was measured in a temperature range from 300 to 700°C. The LTGA crystals that were grown/annealed in the N2 atmosphere showed higher resistivity by 1 order of magnitude as compared to those crystals grown/annealed in the O 2 atmosphere. Based on these results, we suggest that the difference in resistivity is due to the concentration of oxygen vacancy and interstitial oxygen ions. © (2013) Trans Tech Publications.
  English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.566.81
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84883499654&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84883499654&origin=inward
  DOI ID：10.4028/www.scientific.net/KEM.566.81, ISSN：1013-9826, eISSN：1662-9795, ORCID：47804462, SCOPUS ID：84883499654, Web of Science ID：WOS:000324451300018
• Highly tunable transparent-comb-electrode photonic crystals based on Al-doped ZnO/(Pb,La)(Zr,Ti)O₃ multilayer　　　　　　　　　　　　　　　
  Jong-Min Oh; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Applied Physics Express, Volume：6, Number：6, First page：062001, Jun. 2013, [Reviewed]
  We fabricated tunable photonic crystals (PCs) advanced using the electro-optic (EO) effect. These PCs are composed of transparent Al-doped ZnO (AZO) layers as internal/external electrodes and centered (Pb,La)(Zr,Ti)O 3 (PLZT) layers as EO material to use the longitudinal EO effect enabling a large refractive index variations at low voltage to be obtained. The PCs consisting of four periods of AZO/PLZT multilayer were prepared by RF magnetron sputtering. The PCs exhibited a large refractive index change of 2.9 × 10-2 at 8 V, resulting in a high photonic band gap tunability of ∼1 nm/V. © 2013 The Japan Society of Applied Physics.
  English, Scientific journal
  DOI：https://doi.org/10.7567/APEX.6.062001
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84880885135&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84880885135&origin=inward
  DOI ID：10.7567/APEX.6.062001, ISSN：1882-0778, eISSN：1882-0786, ORCID：47804461, SCOPUS ID：84880885135, Web of Science ID：WOS:000320167300010
• Calcium aluminate silicate Ca₂Al₂SiO₇ single crystal applicable to piezoelectric sensors at high temperature　　　　　　　　　　　　　　　
  Hiroaki Takeda; Manabu Hagiwara; Hiroaki Noguchi; Takuya Hoshina; Tomoko Takahashi; Nobuhiro Kodama; Takaaki Tsurumi
  APPLIED PHYSICS LETTERS, Volume：102, Number：24, First page：242907, Jun. 2013, [Reviewed], [Lead, Corresponding]
  Ca2Al2SiO7 (CAS) bulk single crystals were grown by the Czochralski method. Material constants of the crystal were determined over the driving temperature range of a typical combustion pressure sensor. The electrical resistivity at 800 degrees C was found to be of the order of 10 8 Omega cm. We constructed a measurement system for the direct piezoelectric effect at high temperature, and characterized the crystals in a simulated engine cylinder combustion environment. Output charge signal against applied stress was detected at 700 degrees C. These observations suggest that CAS crystals are superior candidate materials for high temperature for stress sensing. (C) 2013 AIP Publishing LLC.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.4811163
  DOI ID：10.1063/1.4811163, ISSN：0003-6951, eISSN：1077-3118, ORCID：47804457, Web of Science ID：WOS:000320962400079
• Influence of Misfit Strain on Longitudinal Electro-optic Properties in Preferentially Oriented (Pb,La)(Zr,Ti)O₃ Films　　　　　　　　　　　　　　　
  Jong-Min Oh; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：52, Number：3, First page：035801, Mar. 2013, [Reviewed]
  We successfully fabricated single-crystal-like (Pb,La)(Zr,Ti)O-3 (PLZT) films with preferred (100), (110), and (111) orientations on Al-doped ZnO (AZO) coated on (100), (110), and (111) SrTiO3 (ST) substrates. The longitudinal electro-optic (LEO) effect according to crystal orientation was investigated to find the birefringence origin of the LEO effect in oriented PLZT films. The PLZT films with (100) and (111) orientations exhibit promising LEO properties, while in the case of (110)-oriented PLZT films, the LEO effect is very small. From the strain-induced EO effect, this difference in LEO properties in these three kinds of preferentially oriented PLZT films may be attributed to changes in the strain effect from in the PLZT/AZO interfaces. Consequently, we believed that a misfit strain in interfaces between EO films and transparent conductive oxide films is a birefringence origin in oriented films, and control of the misfit strain is a key factor for improving the LEO effect. (c) 2013 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.7567/JJAP.52.035801
  DOI ID：10.7567/JJAP.52.035801, ISSN：0021-4922, ORCID：47804463, Web of Science ID：WOS:000315668900038
• Bulk and conductive mode investigations of Pb free PTCR ceramics with high switch temperature　　　　　　　　　　　　　　　
  Mohammad A. Zubair; Hiroaki Takeda; Colin Leach; Robert Freer; Takuya Hoshina; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：121, First page：268, Last page：272, Mar. 2013, [Reviewed], [Corresponding]
  Lead free positive temperature coefficient of resistivity (PTCR) thermistors with switching temperature T-S of 155 degrees C were synthesized from 0.95BaTiO(3)-0.05(Bi1/2K1/2)TiO3 solid solution for high temperature applications, utilizing the conventional ceramic fabrication technique, which involved sintering ceramics in N-2 flow followed by air annealing. Addition of sintering aid AST (Al2O3:SiO2:TiO2 with 4:9:3 molar ratio) and Mn improved the bulk PTCR response. Impedance spectroscopy analysis confirmed the bulk T-S and revealed a third ferroelectric resistance-capacitance (RC) element along with a semiconducting grain and PTCR active ferroelectric grain boundary. The investigation of local electrical activity adopting hot-stage conductive mode microscopy revealed the existence of type-I grain boundary-electron beam induced current (GB-EBIC) contrast pertinent to the presence of negatively charged interfaces neighbored with compensating positive space-charge layers typical of double Schottky barrier within the Pb free PTCR system. (C)2013 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.121.268
  DOI ID：10.2109/jcersj2.121.268, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804455, Web of Science ID：WOS:000316771200003
• High electro-optic kerr effect in (Bi,K,Na)TiO₃ relaxor single crystals　　　　　　　　　　　　　　　
  Kotaro Takeda; Takuya Hoshina; Hiroaki Takeda; Yuji Noguchi; Masaru Miyayama; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：120, First page：613, Last page：615, Dec. 2012, [Reviewed], [Corresponding]
  This report discloses the electro-optic (EO) properties of a lead-free Bi-0.5(K0.33Na0.67)(0.5)TiO3 (33BKNT) single crystal. The 33BKNT single crystal has near zero initial birefringence at room temperature and is optically isotropic. Moreover, the temperature dependence of the crystal's dielectric permittivity reveals its relaxor behavior. The 33BKNT single crystal shows a quadratic EO effect with an EO coefficient (Kerr coefficient) of 16 x 10(-17) m(2)/V-2, which is higher than the Kerr coefficient in other lead-free EO materials at room temperature. (C)2012 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.120.613
  DOI ID：10.2109/jcersj2.120.613, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804470, Web of Science ID：WOS:000312978400012
• Electro-optic effect of lithium niobate in piezoelectric resonance　　　　　　　　　　　　　　　
  Kotaro Takeda; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF APPLIED PHYSICS, Volume：112, Number：12, First page：124105, Dec. 2012, [Reviewed]
  The electro-optic (EO) effect of a lithium niobate (LN) single crystal was analyzed around a piezoelectric resonance frequency. The EO-coefficient of the LN resonator was measured as a function of frequency. The EO-coefficient around piezoelectric resonance frequency varied with a maximum and a minimum in the frequency dependence. To explain the frequency dependence of the EO-coefficient, three effects were considered: (1) the intrinsic EO-effect excluding the effect of piezoelectric resonance, (2) the change of optical pass length due to piezoelectric displacement, and (3) the photo-elastic effect due to piezoelectric strain. The maximum of the EO-coefficient corresponded to the maximum of piezoelectric displacement at the resonance frequency, while the minimum was caused by the phase-lag between applied sinusoidal electric field and piezoelectric displacement. A new equation including the three effects as well as the phase-lag was formulated to represent the EO-effect of piezoelectric crystals. The equation gave a good agreement in the fitting of calculation to the observation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769306]
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.4769306
  DOI ID：10.1063/1.4769306, ISSN：0021-8979, ORCID：47804468, Web of Science ID：WOS:000312829400091
• Local Structure Analysis of Bi₂WO₆　　　　　　　　　　　　　　　
  Yasuhiro Yoneda; Shinji Kohara; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：51, Number：9, First page：09LE06, Sep. 2012, [Reviewed]
  A local structure analysis of Bi2WO6 was performed by high-energy X-ray atomic pair-distribution function (PDF) analysis. We found a deviation between the local and average structures owing to the different coherence lengths between the Bi2O2 and WO6 layers. Bi atoms were displaced toward the b-axis of the orthorhombic P ca2(1) structure. The local off-center shift of Bi atoms coupled with the thermal factor but not with the average structure and thus was neglected. The coherence length of the Bi2O2 layer increased with increasing temperature and spread in the whole crystal when the average structure changed from the P ca2(1) structure to the Aba2 structure. (c) 2012 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.51.09LE06
  DOI ID：10.1143/JJAP.51.09LE06, ISSN：0021-4922, ORCID：47804472, Web of Science ID：WOS:000309007900054
• Identicalness between Piezoelectric Loss and Dielectric Loss in Converse Effect of Piezoelectric Ceramic Resonators　　　　　　　　　　　　　　　
  Manabu Hagiwara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：51, Number：9, First page：09LD10, Sep. 2012, [Reviewed]
  The relationship between piezoelectric loss (tan delta(P)) and dielectric loss (tan delta(E)) in the converse piezoelectric effect in piezoelectric ceramics was investigated theoretically and experimentally. The theoretical consideration was based on the assumption that strain should be proportional to polarization without phase delay in both the intrinsic contribution due to lattice deformation and the extrinsic contribution due to domain wall motion. It was expected that the piezoelectric loss in the converse piezoelectric effect should be identical to the dielectric loss. In order to experimentally verify the identicalness between the losses, the immittance curves of the piezoelectric response of various Pb(Zr, Ti) O-3-based ceramic resonators were fitted if the piezoelectric loss tan delta(P) (1) is equal to zero, (2) exists as the independent variable, and (3) is the same as the dielectric loss tan delta(E). The observation result clearly proved that tan delta(P) is identical to tan delta(E). This identicalness was also demonstrated by analyzing the phase angle of vibration velocity in mechanical response. (C) 2012 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.51.09LD10
  DOI ID：10.1143/JJAP.51.09LD10, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804471, Web of Science ID：WOS:000309007900042
• Grain Size Effect on Dielectric Properties of Ba(Zr,Ti)O₃ Ceramics　　　　　　　　　　　　　　　
  Takuya Hoshina; Tsutomu Furuta; Takahiro Yamazaki; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：51, Number：9, First page：09LC04, Sep. 2012, [Reviewed]
  We demonstrated the size effect on the dielectric properties of BaZrxTi1-xO3 (x = 0.2 and 0.25) ceramics that showed relaxor behavior. Fine-grained BaZrxTi1-xO3 ceramics with micrometer- and nanometer-sized grains were fabricated by the two-step sintering method and aerosol deposition (AD) method, respectively. From the dielectric measurement, the permittivity of the BaZrxTi1-xO3 ceramics markedly decreased with decreasing grain size below 3 mu m. The permittivity of the BaZrxTi1-xO3 nanograined ceramics decreased with increasing Zr content and was much smaller than the permittivity of the BaTiO3 nanograined ceramics. These results indicated that the BaZrxTi1-xO3 ceramics were more susceptible to the grain size effect than the pure BaTiO3 ceramics. The dielectric responses to temperature and frequency suggested that the volume fraction of polar nanoregions decreased and the relaxor characteristics increased with decreasing grain size in BaZrxTi1-xO3 ceramics. (C) 2012 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.51.09LC04
  DOI ID：10.1143/JJAP.51.09LC04, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804469, Web of Science ID：WOS:000309007900027
• Analysis of Vibration Waveforms of Electromechanical Response to Determine Piezoelectric and Electrostrictive Coefficients　　　　　　　　　　　　　　　
  Tatsuya Izumi; Manabu Hagiwara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Volume：59, Number：8, First page：1632, Last page：1638, Aug. 2012, [Reviewed]
  We developed a possible method to determine both coefficients of piezoelectricity (d) and electrostriction (M) at the same time by a waveform analysis of current and vibration velocity in the resonance state. The waveforms of the current and vibration velocity were theoretically described using the equations of motion and piezoelectric constitutive equations, considering the dissipation effect. The dissipation factor of the d coefficient and M coefficient is dielectric loss tangent tan delta. The waveforms measured in all of the ceramics, such as Pb(Zr,Ti)O-3 (PZT), Pb(Mg,Nb)O-3 (PMN), and 0.8Pb(Mg1/3Nb2/3)O-3-0.2PbTiO(3) (PMN-PT), were well fitted with the calculated waveform. This fitting produced both the d and M coefficients, which agreed with those determined via the conventional methods. Moreover, the respective contributions of both piezoelectricity and electrostriction to the d value determined in the resonance-antiresonance method were clarified.
  IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, English, Scientific journal
  DOI：https://doi.org/10.1109/TUFFC.2012.2369
  DOI ID：10.1109/TUFFC.2012.2369, ISSN：0885-3010, ORCID：47804467, Web of Science ID：WOS:000307831900004
• Quasi-millimeter-wave absorption behavior in Y/Yb-stabilized zirconia ceramics　　　　　　　　　　　　　　　
  Takashi Teranishi; Naoki Akiyama; Keiko Ayano; Hidetaka Hayashi; Akira Kishimoto; Kazuhiro Fujimori; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  APPLIED PHYSICS LETTERS, Volume：100, Number：24, First page：242903, Jun. 2012, [Reviewed]
  Broadband dielectric spectra from 10 to 10(14) Hz were acquired for 8 mol. % Y2O3/Yb2O3-stabilized zirconia (8YSZ and 8YbSZ) ceramics that related the dipole and ionic polarization losses to the absorption efficiency of electromagnetic irradiation. For 24 GHz irradiation, 8YSZ exhibited a higher absorption efficiency than 8YbSZ, resulting in a higher dielectric loss. The difference in the dielectric loss was interpreted as the difference in the loss of the dipoles originating from the fluctuations in the defect associations (Y'(Zr)Vo and Yb'(Zr)Vo). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729147]
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.4729147
  DOI ID：10.1063/1.4729147, ISSN：0003-6951, ORCID：47804474, Web of Science ID：WOS:000305269200056
• Longitudinal electro-optic effect of highly (100) oriented (Pb,La)(Zr,Ti)O₃ film grown on a transparent Al-doped ZnO electrode　　　　　　　　　　　　　　　
  Jong-Min Oh; Kotaro Takeda; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：120, First page：166, Last page：170, May 2012, [Reviewed]
  The highly (100) oriented (Pb,La)(Zr,Ti)O-3 (PLZT) films were successfully grown on (110) Al-doped ZnO (AZO) coated on (100) SrTiO3 (ST) substrates using an RF magnetron sputter. The ferroelectric, dielectric, and optical properties of the transparent AZO/PLZT/AZO/ST structure were investigated to suggest the feasibility of AZO as an alternative transparent conductive oxide (TCO) electrode for optical devices requiring the longitudinal electro-optic (EO) effect. Recorded P-E loops showed slim hysteresis, and the remanent polarization and coercive field were 6.5 mu C/cm(2) and 37 kV/cm. The relative permittivity and loss tangent were 745 and 0.044 at 10 kHz, respectively. The optical transmittance of the structure was over 90% in the near-infrared (NIR) region. Finally, the AZO/PLZT/AZO films grown on the ST substrate exhibited a strong quadratic EO effect and the longitudinal EO coefficient was 180 nm(2)/V-2 at lambda = 1550nm. (C) 2012 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.120.166
  DOI ID：10.2109/jcersj2.120.166, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804473, Web of Science ID：WOS:000304226200002
• Fabrication of lead-free semiconducting ceramics using a BaTiO₃-(Bi_1/2Na_1/2)TiO₃ system by adding CaO　　　　　　　　　　　　　　　
  Takashi Tateishi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：119, First page：828, Last page：831, Nov. 2011, [Reviewed], [Corresponding]
  BaTiO3-(Bi1/2Na1/2)TiO3 (abbreviated as BT-BNT) solid solution semiconducting ceramics, as a candidate for a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor usable over 130 degrees C, were synthesized by adding CaO into the calcined powder. The CaO added BT-BNT ceramics showed semiconducting behavior with the resistivity at room temperature rho(RT) = 10(3) Omega cm and a resistivity change near Curie temperature. Chemical composition analysis suggested that Ca2+ acted as a donor by substituting for Na+ in the BT-BNT ceramics. (C) 2011 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.119.828
  DOI ID：10.2109/jcersj2.119.828, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804481, Web of Science ID：WOS:000297279300011
• Shrinkage Behaviors and Sintering Mechanism of BaTiO₃ Ceramics in Two-Step Sintering　　　　　　　　　　　　　　　
  Takuya Hoshina; Yoichi Kigoshi; Tsutomu Furuta; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：50, Number：9, First page：09NC07, Sep. 2011, [Reviewed]
  The shrinkage behaviors of BaTiO3 ceramics in a nonisothermal process were quantitatively monitored to clarify the mechanism of two-step sintering. During the increase in temperature, shrinkage behaviors due to grain boundary diffusion, volume diffusion, and grain rearrangement were observed. From the analysis of the shrinkage curve and the observation of the microstructure, the first step in two-step sintering was interpreted as a process for eliminating large pores by grain rearrangement. In contrast, the second step was interpreted as a process for final densification by volume diffusion. It was clarified that the analysis of shrinkage behaviors was useful for understanding two-step sintering and for determining suitable sintering conditions. (C) 2011 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.50.09NC07
  DOI ID：10.1143/JJAP.50.09NC07, ISSN：0021-4922, ORCID：47804484, Web of Science ID：WOS:000295032000021
• Effect of Material Constants on Power Output in Piezoelectric Vibration-Based Generators　　　　　　　　　　　　　　　
  Hiroaki Takeda; Kensuke Mihara; Tomohiro Yoshimura; Takuya Hoshina; Takaaki Tsurumi
  IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Volume：58, Number：9, First page：1852, Last page：1859, Sep. 2011, [Reviewed], [Lead, Corresponding]
  A possible power output estimation based on material constants in piezoelectric vibration-based generators is proposed. A modified equivalent circuit model of the generator was built and was validated by the measurement results in the generator fabricated using potassium sodium niobate-based and lead zirconate titanate (PZT) ceramics. Subsequently, generators with the same structure using other PZT-based and bismuth-layered structure ferroelectrics ceramics were fabricated and tested. The power outputs of these generators were expressed as a linear functions of the term composed of electromechanical coupling coefficients k(sys)(2) and mechanical quality factors Q(m)* of the generator. The relationship between device constants (k(sys)(2) and Q(m)*) and material constants (k(31)(2) and Q(m)) was clarified. Estimation of the power output using material constants is demonstrated and the appropriate piezoelectric material for the generator is suggested.
  IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, English, Scientific journal
  DOI：https://doi.org/10.1109/TUFFC.2011.2023
  DOI ID：10.1109/TUFFC.2011.2023, ISSN：0885-3010, eISSN：1525-8955, ORCID：47804478, Web of Science ID：WOS:000295101600017
• Analysis of Nonlinear Transient Responses of Piezoelectric Resonators　　　　　　　　　　　　　　　
  Manabu Hagiwara; Seita Takahashi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Volume：58, Number：9, First page：1721, Last page：1729, Sep. 2011, [Reviewed]
  The electric transient response method is an effective technique to evaluate material constants of piezoelectric ceramics under high-power driving. In this study, we tried to incorporate nonlinear piezoelectric behaviors in the analysis of transient responses. As a base for handling the nonlinear piezoelectric responses, we proposed an assumption that the electric displacement is proportional to the strain without phase lag, which could be described by a real and constant piezoelectric e-coefficient. Piezoelectric constitutive equations including nonlinear responses were proposed to calculate transient responses of a piezoelectric resonator. The envelopes and waveforms of current and vibration velocity in transient responses observed in some piezoelectric ceramics could be fitted with the calculation including nonlinear responses. The procedure for calculation of mechanical quality factor Q(m) for piezoelectric resonators with nonlinear behaviors was also proposed.
  IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, English, Scientific journal
  DOI：https://doi.org/10.1109/TUFFC.2011.2009
  DOI ID：10.1109/TUFFC.2011.2009, ISSN：0885-3010, ORCID：47804475, Web of Science ID：WOS:000295101600003
• The effect of oxygen vacancies on the dielectric responses of BaTiO₃ based ceramics in the ultra-wide frequency range　　　　　　　　　　　　　　　
  Youn-Kyu Choi; Takuya Hoshina; Hiroaki Takeda; Jong-Min Oh; Takaaki Tsurumi
  Key Engineering Materials, Volume：485, First page：15, Last page：18, Jul. 2011, [Reviewed]
  The effect of oxygen vacancies and their migrations on the dielectric responses of BaTiO3 (BT) ceramics and (Ba, Ca)(Ti, Zr)O-3 (BCTZ) ceramics was studied using wideband dielectric spectroscopy. Both dipole and ionic polarization of BT ceramics after annealing in a reducing atmosphere markedly decreased. To elucidate the decrease of dipole and ionic polarization, we observed the domain width and the crystal structure of BT ceramics annealed in different PO2. The mass fractions of constituted phases in 90 degrees domain were calculated using the refinement of XRD patterns to explain the degradation of ionic polarization by oxygen vacancies. From the results above, we judged that the decrease of dipole polarization was due to the domain wall clamping by oxygen vacancies, while that of ionic polarization was attributable to the lattice hardening by the incorporation of oxygen vacancies into the BT lattice. In the case of BCTZ ceramics, dipole polarization showed the same way as BT ceramics with annealing conditions but the ionic polarization was independent of PO2 in annealing because of anti-reducing behavior of BCTZ ceramics. On the basis of the effect of oxygen vacancy in BT ceramics and BCTZ ceramics, we could clarify the oxygen vacancy migration in BCTZ ceramics under high direct-current voltage (DCV).
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.485.15
  DOI ID：10.4028/www.scientific.net/KEM.485.15, ISSN：1013-9826, ORCID：47804485, Web of Science ID：WOS:000309191700004
• Influence of Schottky interfaces on dielectric properties in perovskite-type oxide thin-film capacitors　　　　　　　　　　　　　　　
  Naohiro Horiuchi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：485, First page：203, Last page：206, Jul. 2011, [Reviewed]
  An estimation method of the influence of interfaces on properties in perovskite-type oxide thin-film capacitors is presented. We proposed a modified Schottky model that can be employed to explain the electric properties of metal/perovskite-type oxide junctions. The modified model considers the electric field dependence of permittivity and the flow of electrons from metal to defect states located in the band gap of the perovskite oxide. The simulation based on this model could successfully describe the results of capacitance-voltage measurements of junctions between metals (Pt, Au, and Ag) and Nb-doped SrTiO3, which were not explained by the conventional Schottky model. Additionally, a simulation for a thin-film capacitor with hysteretic behavior could depict an asymmetric capacitance-voltage curve.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.485.203
  DOI ID：10.4028/www.scientific.net/KEM.485.203, ISSN：1013-9826, ORCID：47804483, Web of Science ID：WOS:000309191700049
• Fabrication of Lead-free Semiconducting Ceramics Using BaTiO₃-(Bi_1/2Na_1/2)TiO₃ System by Sintering in Air Atmosphere　　　　　　　　　　　　　　　
  Takashi Tateishi; Han Joong-Sang; Hiroaki Takeda; Takuya Hoshina; Spela Kunej; Takaaki Tsurumi
  Key Engineering Materials, Volume：485, First page：245, Last page：248, Jul. 2011, [Reviewed]
  BaTiO3-(Bi1/2Na1/2)TiO3 (abbreviated as BT-BNT) solid solution ceramics, as a lead-free PTC (Positive Temperature Coefficient of resistivity) thermistor material usable over 130 degrees C, were synthesized in air atmosphere. By conventional processes, La-doping was not effective in giving semiconducting property to the BT-BNT ceramics because of volatilization of sodium and bismuth during sintering. By preventing the volatilization by lowering the sintering temperature using very fine TiO2 powder and by adding calcium oxide to calcined BT-BNT powders, we obtained BT-BNT semiconducting ceramics which shows a resistivity change near Curie temperature.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.485.245
  DOI ID：10.4028/www.scientific.net/KEM.485.245, ISSN：1013-9826, ORCID：47804482, Web of Science ID：WOS:000309191700059
• Fabrication of BaTiO₃ Films on Si Substrate by Inkjet Printing　　　　　　　　　　　　　　　
  Ai Komatsu; Takuya Hoshina; Spela Kunej; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：485, First page：187, Last page：190, Jul. 2011, [Reviewed]
  BaTiO3 films were fabricated on Si substrate using inkjet printing technique. To achieve low-temperature fabrication of BaTiO3 films, Ba-Ti-alkoxide ink was prepared. The mixing ratio and sequence of raw materials were optimized for controlling the chemical stability and viscosity of alkoxide ink. The inkjet printing films on Si substrate were annealed at 700 degrees C, and it resulted in the formation of BaTiO3. It was found that the film quality was improved by adding BaTiO3 nanoparticles into the Ba-Ti-alkoxide ink.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.485.187
  DOI ID：10.4028/www.scientific.net/KEM.485.187, ISSN：1013-9826, ORCID：47804480, Web of Science ID：WOS:000309191700045
• Dielectric Properties of Nanograined BaTiO₃ Ceramics Fabricated by Aerosol Deposition Method　　　　　　　　　　　　　　　
  Tsutomu Furuta; Saki Hatta; Yoichi Kigoshi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：485, First page：183, Last page：186, Jul. 2011, [Reviewed]
  Freestanding BaTiO3 ceramics films were fabricated using the aerosol deposition (AD) method and the size effect of nanograined BaTiO3 ceramics was demonstrated. Dense BaTiO3 thick film fabricated by the AD method was crystallized and detached from substrate by an annealing treatment at 600 degrees C, and then the grain size was controlled by a reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization-electric field (P-E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range of 170 to 24 nm.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.485.183
  DOI ID：10.4028/www.scientific.net/KEM.485.183, ISSN：1013-9826, ORCID：47804477, Web of Science ID：WOS:000309191700044
• Characterization of Grain Boundaries of Lead-free Semiconducting Ceramics Using BaTiO₃-(Bi_1/2K_1/2)TiO₃ System　　　　　　　　　　　　　　　
  Hiroaki Takeda; Joong-Sang Han; Takashi Tateishi; Spela Kunej; Colin Leach; Robert Freer; Takuya Hoshina; Takaaki Tsurumi
  Key Engineering Materials, Volume：485, First page：241, Last page：244, Jul. 2011, [Reviewed], [Lead, Corresponding]
  BaTiO3-(Bi1/2K1/2)TiO3 (abbreviated as BT-BKT) solid solution ceramics, as a lead-free PTC (positive temperature coefficient of resistivity) thermistor material usable over 130 degrees C, has been synthesized by sintering in N-2 atmosphere and after annealing in air over 1200 degrees C. In the BT-BKT ceramics with PTC property, the impedance/modulus spectroscopic plots have revealed that a third resistance-capacitance (RC) response besides grains and grain boundaries. Using the remote electron beam induced current (REBIC) configuration, imaging has revealed EBIC contrast consistent with the presence of negatively charged electrostatic grain boundary barriers in the BT-BKT semiconducting ceramics.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.485.241
  DOI ID：10.4028/www.scientific.net/KEM.485.241, ISSN：1013-9826, ORCID：47804476, Web of Science ID：WOS:000309191700058
• Effect of Oxygen Vacancy and Oxygen Vacancy Migration on Dielectric Response of BaTiO₃-Based Ceramics　　　　　　　　　　　　　　　
  Youn-Kyu Choi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：50, Number：3, First page：031504, Mar. 2011, [Reviewed]
  The effects of oxygen vacancies and their migrations on the dielectric responses of pure BaTiO3 (BT) ceramics and (Ba0.9Ca0.1)(1.01)(Ti0.9Zr0.1)O-3 (BCTZ) ceramics, where portions of Ba and Ti were respectively substituted with Ca and Zr, were studied using wideband dielectric spectroscopy. The decrease in the dipole polarization of BT ceramics after annealing in a reducing atmosphere was due to domain-wall clamping by oxygen vacancies, while that of ionic polarization was attributable to lattice hardening by the incorporation of oxygen vacancies into the BT lattices. The dipole polarization of BCTZ ceramics indicated the same change as did that of BT ceramics after annealing, but the ionic polarization was independent of PO2 in annealing because of the anti-reducing behavior of BCTZ ceramics. The oxygen vacancy migration in BCTZ ceramics could be detected as a change of wideband dielectric spectra. The change observed only in the dipole polarization could be explained the oxygen vacancy migration from the anode to the cathode. (C) 2011 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.50.031504
  DOI ID：10.1143/JJAP.50.031504, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804479, Web of Science ID：WOS:000288649800027
• Size Effect and Domain-Wall Contribution of Barium Titanate Ceramics　　　　　　　　　　　　　　　
  Takuya Hoshina; Yoichi Kigoshi; Saki Hatta; Takashi Teranishi; Hiroaki Takeda; Takaaki Tsurumi
  FERROELECTRICS, Volume：402, Number：1, First page：29, Last page：36, Nov. 2010, [Reviewed]
  Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 m were prepared by a conventional sintering method and a two-step sintering method. The permittivity of the BaTiO3 ceramics with an average grain size of 1.1 m exhibited a maximum around 8,000. By ultrawide range dielectric spectroscopy, the domain-wall contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 m, the dipole and ionic polarizabilities were enhanced by the high domain density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 m, these polarizabilities were weakened.
  TAYLOR & FRANCIS LTD, English, Scientific journal
  DOI：https://doi.org/10.1080/00150191003697179
  DOI ID：10.1080/00150191003697179, ISSN：0015-0193, eISSN：1563-5112, ORCID：47804504, Web of Science ID：WOS:000284477300005
• Effects of oxygen vacancies and grain sizes on the dielectric response of BaTiO₃　　　　　　　　　　　　　　　
  Youn-Kyu Choi; Takuya Hoshina; Hiroaki Takeda; Takeshi Teranishi; Takaaki Tsurumi
  APPLIED PHYSICS LETTERS, Volume：97, Number：21, First page：212907, Nov. 2010, [Reviewed]
  The effects of grain size and oxygen vacancies on the dielectric responses of BaTiO3 ceramics were investigated using wideband dielectric spectroscopy. Both dipole and ionic polarizations were enhanced by the reduction in grain size down to 2.5 mu m. The annealing in low oxygen partial pressure markedly suppressed the dipole polarization possibly due to the domain-wall clamping by oxygen vacancies. To explain the dielectric response of BaTiO3 ceramics, a complex structure including gradient lattice strain layers (GLSL) were proposed as a model of 90 degrees domain structure. (C) 2010 American Institute of Physics. [doi:10.1063/1.3508947]
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.3508947
  DOI ID：10.1063/1.3508947, ISSN：0003-6951, ORCID：47804493, Web of Science ID：WOS:000284618300040
• Effects of Ca and Zr additions and stoichiometry on the electrical properties of barium titanate-based ceramics　　　　　　　　　　　　　　　
  Youn Kyu Choi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：118, First page：881, Last page：886, Oct. 2010, [Reviewed]
  (Ba1-xCax)(m)(Ti1-yZry)O-3 (BCTZ-x-y-m) ceramics were studied to clarify the effects of Ca and/or Zr addition and the non-stoichiometry of BCTZ ceramics. The range of each element was 0.00 <= x,y <= 0.25 and 0.995 <= m <= 1.02. All powders were prepared by a solid state reaction method. Green bodies with disc shapes were sintered at 1500 degrees C for 2 h in air and then reheated at 950 degrees C for 5h in various reducing conditions. The dielectrics with the substitution of Ca ion in BCTZ-x-0.0-1.01 (x <= 0.10) showed an increase in T-c and the insulation resistivity improved with increasing x. The increase of Zr content (y) in BCTZ-0.1-y-1.01 and m in BCTZ-0.1-0.1-m led to the phase transition of dielectrics to relaxors, accompanying the decrease of T-c. In BCTZ-0.1-0.1-m, Ca and Zr co-doped dielectrics showed a high insulation resistivity (IR), even though m = 1.00. There are two possible origins of the higher resistivity observed in BCTZ with m = 1.0. The first is the acceptor action of Ca ions that moved from Ba sites to Ti sites in BaTiO3; the second is the higher charge stability of the Zr ion than that of the Ti ion in a reducing atmosphere. (C) 2010 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.118.881
  DOI ID：10.2109/jcersj2.118.881, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804492, Web of Science ID：WOS:000283412100006
• Analysis of Polarization Behavior in Relaxation of BaTiO₃-Based Ferroelectrics Using Wideband Dielectric Spectroscopy　　　　　　　　　　　　　　　
  Takashi Teranishi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Volume：57, Number：10, First page：2118, Last page：2126, Oct. 2010, [Reviewed]
  Wideband dielectric spectra from the kilohertz to terahertz range are discussed for BaTiO3-based ferroelectrics. Ceramics of BaTiO3 (BT), Ba0.6Sr0.4TiO3 (BST-0.6), and BaZr0.25Ti0.75O3 (BZT-0.25) were selected as normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics), and relaxor ferroelectrics, respectively. The variation of ionic polarization in both BT and BST-0.6 ceramics with temperature could be explained by the softening of the soft phonon mode. In BZT-0.25, a permittivity anomaly at the dielectric maximum temperature (T-m) at low frequencies is not attributed to the softening of the soft phonon mode, but originates from the permittivity derived from the dipole polarization (epsilon(dipole)). Relaxor behavior in BZT-0.25 is derived from the increase in the depression of epsilon(dipole) on cooling across the T-m with increasing frequency. In dipole polarization, BT, BST0.6, and BZT-0.25 all exhibited a similar tendency of epsilon(dipole) above the Curie temperature (T-c) and T-m. However, behavior of epsilon(dipole) below the T-c can be explained by the ferroelectric domains in BT, whereas the variation of epsilon(dipole) below the T-m could be explained by growth process of polar nanoregions (PNRs) in BST-0.6 and BZT-0.25. Regarding this, BT can be distinguished from BST-0.6 and BZT-0.25. Relaxation in BT could be interpreted as successive change in polarization mechanism from normal ferroelectrics to relaxor ferroelectrics via DPT ferroelectrics.
  IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, English, Scientific journal
  DOI：https://doi.org/10.1109/TUFFC.2010.1667
  DOI ID：10.1109/TUFFC.2010.1667, ISSN：0885-3010, ORCID：47804486, Web of Science ID：WOS:000283366000002
• Size Effect of Nanograined BaTiO₃ Ceramics Fabricated by Aerosol Deposition Method　　　　　　　　　　　　　　　
  Takuya Hoshina; Tsutomu Furuta; Yoichi Kigoshi; Saki Hatta; Naohiro Horiuchi; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：49, Number：9, First page：09MC02, Sep. 2010, [Reviewed]
  We demonstrated the size effect of nanograined BaTiO3 ceramics using freestanding BaTiO3 thick films fabricated by the aerosol deposition (AD) method. Dense BaTiO3 thick films fabricated by the AD method were crystallized and detached from the SrTiO3 substrate by annealing treatment at 600 degrees C, and then the grain size was controlled by reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization-electric field (P-E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range from 170 to 24 nm. The decrease in permittivity was due to the decreases in ferroelectricity and domain-wall contributions with decreasing grain size. (C) 2010 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.49.09MC02
  DOI ID：10.1143/JJAP.49.09MC02, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804505, Web of Science ID：WOS:000282137100023
• Nonlinear Shear Responses of Lead Zirconate Titanate Piezoelectric Ceramics　　　　　　　　　　　　　　　
  Manabu Hagiwara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：49, Number：9, First page：09MD04, Sep. 2010, [Reviewed]
  The nonlinear piezoelectric and dielectric responses in the shear mode against an applied field were investigated using hard and soft Pb(Zr, Ti)O-3 (PZT)-based piezoelectric ceramics. The shear strain was measured using a double-beam leaser Doppler vibrometer. The third-order harmonic components of the strain and the current of soft PZT markedly increased with the increase in the field while those of hard PZT were maintained at low values. In hard PZT, the elastic nonlinearity in the shear mode was also estimated by measuring the change in fundamental resonance frequency. This nonlinearity showed a small dependence on the strain compared with that in the length-extensional mode. (C) 2010 The Japan Society of Applied Physics
  IOP PUBLISHING LTD, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.49.09MD04
  DOI ID：10.1143/JJAP.49.09MD04, ISSN：0021-4922, eISSN：1347-4065, ORCID：47804502, Web of Science ID：WOS:000282137100038
• The influence of metal/perovskite-type oxide interfaces on tunability of thin film capacitors　　　　　　　　　　　　　　　
  Naohiro Horiuchi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：118, First page：664, Last page：668, Aug. 2010, [Reviewed]
  We propose a calculation model that can predict the influence of Interface on capacitance-voltage characteristics of metal-insulator-metal type thin film capacitor with perovskite type oxide. The simulation could successfully describe the results of capacitance-voltage measurements of the barium strontium titanate thin film capacitors with top electrodes of Pt, Au, and Ag. It is found that the electrode dependent on the tunability is derived from the work function of the electrode metal. The simulation model is base on the Schottky model that can be employed to explain the dielectric properties of metal/perovskite type oxide junction. The modified Schottky model considers the electric field dependence of permittivity and the back flow of electrons from metal to defect states located in the band gap of the perovskite oxide. This flow forms negatively charged space at the interface and affects the electric properties of the thin film capacitors. (C) 2010 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.118.664
  DOI ID：10.2109/jcersj2.118.664, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804506, Web of Science ID：WOS:000281229200010
• Cation distribution and piezoelectric properties of aluminum substituted La₃Ta_0.5Ga_5.5O₁₄ single crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Jun-ichi Yamaura; Takuya Hoshina; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：118, First page：706, Last page：710, Aug. 2010, [Reviewed], [Lead, Corresponding]
  We report the structure and electric properties of La3Ta0.5Ga5.5-xAlxO14 (LTGAx, x = 0.0 (LTG), 0.3 and 0.5) single crystals, with a Ca3Ga2Ge4O14-type structure, suitable for high temperature piezoelectric application. A single-crystal X-ray structure analysis reveals that Al atoms are distributed in all cation sites except for the decahedral site occupied by La, which favors instead the octahedral site. The piezoelectric moduli d(11) kept a constant, whereas vertical bar d(14)vertical bar increased 14% with the increasing Al content, x, up to 0.5. The LTGA0.5 crystals showed a low temperature dependence (2% deviation from room temperature to 400 degrees C) of d(11) and a higher electric resistivity rho than those of the LTG crystals. The Al substitution is effective for improving the electrical properties of the LTG. (C) 2010 The Ceramic Society of Japan All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.118.706
  DOI ID：10.2109/jcersj2.118.706, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804488, Web of Science ID：WOS:000281229200019
• Analysis on dipole polarization of BaTiO₃-based ferroelectric ceramics by Raman spectroscopy　　　　　　　　　　　　　　　
  Takashi Teranishi; Naohiro Horiuchi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：118, First page：679, Last page：682, Aug. 2010, [Reviewed]
  Analysis of asymmetric Raman line shape disclosed the variation of phonon correlation length in A(1)(3TO) mode, L-A1(3TO), with temperature in the ceramics of BaTiO3 (BT), Ba0.6Sr0.4TiO3 (BST-0.6) and BaZr0.25Ti0.75O3 (BZT-0.25), namely normal ferroelectrics, ferroelectrics with diffuse phase transition (DPT ferroelectrics) and relaxor ferroelectrics, respectively. In BT, L-A1(3TO) exhibited steep increase at the Curie temperature (T-c) on cooling. This is attributed to the formation of the ferroelectric domains at the T-c. Both BST-0.6 and BZT-0.25 showed gradual increase in L-A1(3TO) on cooling across the dielectric maximum temperature (T-m), indicating the continuous increase in the average size of the polar nanoregions (PNRs). Normal ferroelectrics can be distinguished from DPT and relaxor ferroelectrics in this point. L-A1(3TO) of BZT-0.25 was longer than that of BST-0.6 near the T-m. This suggests the size of PNRs in BZT-0.25 is larger than that in BST-0.6. Huge dipole polarization of BZT-0.25, giving rise to the strong relaxor behavior, could be originated from the contribution of the large PNRs near the T-m. DPT ferroelectrics can be also differentiated from relaxor ferroelectrics in terms of the average size of PNRs. (C) 2010 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.118.679
  DOI ID：10.2109/jcersj2.118.679, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804487, Web of Science ID：WOS:000281229200013
• Nonlinear shear response in (K,Na)NbO₃-based lead-free piezoelectric ceramics　　　　　　　　　　　　　　　
  Manabu Hagiwara; Seita Takahashi; Takuya Hoshina; Hiroaki Takeda; Osamu Sakurai; Takaaki Tsurumi
  Key Engineering Materials, Volume：445, First page：47, Last page：50, Jul. 2010, [Reviewed]
  The piezoelectric shear response of 94.0(Ka(0.5), Na-0.5)NbO3 (KNN) + 5.0LiNbO(3) (LN) + 0.5SrTiO(3) (ST) + 0.5BiFeO(3) (BF) ceramics was investigated by Laser Doppler Vibrometry (LDV) and resonance-antiresonance method. From resonance-antiresonance method, the piezoelectric d(15) constant was obtained to be 273 pC/N. The shear strain obtained by LDV at the frequency of 150kHz showed strong nonlinearity. This suggested that the domain contribution to piezoelectric response in shear mode of KNN-LN-ST-BF ceramics existed at the operational frequency for the shear mode divices.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.445.47
  DOI ID：10.4028/www.scientific.net/KEM.445.47, ISSN：1013-9826, ORCID：47804501, Web of Science ID：WOS:000291630900012
• Evolution of Internal Stress and Influence on Dielectric Properties by Number of Dielectric Layers in MLCC　　　　　　　　　　　　　　　
  Satoshi Yokomizo; Takuya Hoshina; Hiroaki Takeda; Katsuya Taniguchi; Youichi Mizuno; Hirokazu Chazono; Osamu Sakurai; Takaaki Tsurumi
  Key Engineering Materials, Volume：445, First page：31, Last page：34, Jul. 2010, [Reviewed]
  We researched the phenomenon that the permittivity of dielectric layers in multilayer ceramic capacitor (MLCC) increases with the number of dielectric layers. Finite element method (FEM) shows that the internal residual stress in MLCC was generated by the difference of thermal expansion coefficient between internal electrodes and dielectric layers. We developed a electric measurement system with applying external stress for understanding the stress influence on dielectric properties. The compressive stress along electric field increased the polarization. The polar nano regions (PNRs) in shell composition dielectrics were easily influenced by stress. Based on these results, the relationship between the number of dielectric layers and their permittivity in MLCCs was explained.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.445.31
  DOI ID：10.4028/www.scientific.net/KEM.445.31, ISSN：1013-9826, ORCID：47804495, Web of Science ID：WOS:000291630900008
• Effect of Metal-Dielectric Interfaces on Tunability in Barium Strontium Titanate Thin-film Capacitor　　　　　　　　　　　　　　　
  Naohiro Horiuchi; Takuya Hoshina; Hiroaki Takeda; Osamu Sakurai; Takaaki Tsurumi
  Key Engineering Materials, Volume：445, First page：140, Last page：143, Jul. 2010, [Reviewed]
  We investigated an influence of interface layer on a tunability of parallel plate (Ba, Sr)TiO3 thin film capacitors. BST thin film capacitors with top electrode of Pt, Au and Ag were fabricated. BST films had thickness of 40, 60, 80 and 120nm. The tunability increased with increasing the BST film thickness. Considering the interfaces between BST films and electrodes as Schottky junctions, depletion layers were formed in the interfaces depending on the difference of the work function of metal electrodes. Larger external bias voltages were applied to the depletion layer than interior BST film, because the permittivity in the depletion layer was smaller than that in interior BST film. Therefore, the depletion layer lowered the tunability. Tunability decreased with increasing the thickness of the depletion layers.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.445.140
  DOI ID：10.4028/www.scientific.net/KEM.445.140, ISSN：1013-9826, ORCID：47804491, Web of Science ID：WOS:000291630900033
• Dielectric Properties of Barium Titanate Ceramics with Nano-Sized Domain　　　　　　　　　　　　　　　
  Yoichi Kigoshi; Saki Hatta; Takashi Teranishi; Takuya Hoshina; Hiroaki Takeda; Osamu Sakurai; Takaaki Tsururni
  Key Engineering Materials, Volume：445, First page：27, Last page：30, Jul. 2010, [Reviewed]
  Barium titanate (BaTiO3) ceramics with various grain sizes from 0.7 to 13 mu m on average were prepared by a conventional sintering method, a two-step sintering method and a rate controlled two-step sintering method. The permittivity of the ceramics was increased with decreasing grain size to 1.1 mu m on average. However, the permittivity of the ceramics was decreased when the grain size was below 1 mu m. The field emission scanning electron microscope (FE-SEM) observations revealed that the 900 domain width decreased with decreasing the grain size. By ultrawide range dielectric spectra from kHz to THz range of the BaTiO3 ceramics, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 mu m, the dipole polarizability and the ionic polarizability were enhanced by high domain-wall density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 mu m, these polarizabilities were weakened.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.445.27
  DOI ID：10.4028/www.scientific.net/KEM.445.27, ISSN：1013-9826, ORCID：47804489, Web of Science ID：WOS:000291630900007
• Growth and piezoelectric properties of ferroelectric Bi₂WO₆ mono-domain crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Joong Sang Han; Masaya Nishida; Tadashi Shiosaki; Takuya Hoshina; Takaaki Tsurumi
  SOLID STATE COMMUNICATIONS, Volume：150, Number：17-18, First page：836, Last page：839, May 2010, [Reviewed], [Lead, Corresponding]
  A mono-domain crystal of Bismuth tungstate Bi2WO6, one of the bismuth layered structure ferroelectric (BLSF) compounds, is synthesized by a slow cooling method using lithium tetra-borate as the flux below the Curie temperature of 940 degrees C. Fifteen of seventeen independent tensor components of dielectric constant epsilon(ij)/epsilon(0), piezoelectric constant d(ij) and elastic compliance s(ij) are determined. The dielectric constants, epsilon(ij)/epsilon(0), were about 100, 70 and 70 for ij = 11, 22 and 33 and the piezoelectric constants, d(31) and d(33) were - 17 and 27 pC/N, respectively. These characteristics are consistent with those of BLSF grain-oriented ceramics. The resonance response revealed that the BWO crystals maintained the piezoelectricity up to 400 degrees C. (C) 2010 Elsevier Ltd All rights reserved.
  PERGAMON-ELSEVIER SCIENCE LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.ssc.2010.02.011
  DOI ID：10.1016/j.ssc.2010.02.011, ISSN：0038-1098, eISSN：1879-2766, ORCID：47804499, Web of Science ID：WOS:000276781600008
• Wide Band Dielectric Spectroscopy at Ferroelectric Phase Transition of BaTiO₃ Ceramics　　　　　　　　　　　　　　　
  Takashi Teranishi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：49, Number：4, First page：0415061, Last page：0415064, Apr. 2010, [Reviewed]
  Ultrawide band dielectric spectra from kHz to THz were measured to investigate quantitatively the contributions of ionic and dipole polarizations to the ferroelectric phase transition in BaTiO3 (BT) ceramics. Permittivity derived from ionic polarization (epsilon(ionic)) exhibited its maximum at the Curie temperature (T-c), attributing to the softening of the soft phonon mode. Permittivity derived from dipole polarization (epsilon(dipole)) was nearly constant below the T-c, while epsilon(dipole) remained above the T-c and epsilon(dipole) increased on cooling, exhibiting its maximum near the T-c. The behavior in epsilon(dipole) above the T-c could be interpreted as precursor phenomenon of ferroelectric phase transition and the epsilon(dipole) above the T-c was due to the local tetragonal type distortion in paraelectric phase. (C) 2010 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.49.041506
  DOI ID：10.1143/JJAP.49.041506, ISSN：0021-4922, ORCID：47804507, Web of Science ID：WOS:000277300700030
• Mechanism Underlying Stacking-Layer Effect of Dielectric Properties of Multilayer Ceramic Capacitors　　　　　　　　　　　　　　　
  Satoshi Yokomizo; Takuya Hoshina; Hiroaki Takeda; Katsuya Taniguchi; Youichi Mizuno; Hirokazu Chazono; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：49, Number：4, First page：0415051, Last page：0415055, Apr. 2010, [Reviewed]
  The stacking-layer effect in multilayer ceramic capacitors (MLCCs) is a phenomenon in which the dielectric permittivity of dielectric layers increases with increasing number of layers. To elucidate the mechanism underlying this effect, we performed a simulation of residual stress in MLCCs by the finite element method (FEM) as well as dielectric measurements under uniaxial compressive stress. The FEM analysis revealed that tensile stress along the stacking direction was induced in dielectric layers owing to the difference in thermal expansion coefficient between internal electrodes and dielectric layers. The results of dielectric measurements indicated that the shell part in the dielectrics of MLCCs played an important role in the stress dependence of dielectric properties. The mechanism underlying the stacking-layer effect proposed in this study was based on the enhancement of polarization rotations in polar nanoregions in the relaxor by the tensile stress in dielectric layers. (C) 2010 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.49.041505
  DOI ID：10.1143/JJAP.49.041505, ISSN：0021-4922, ORCID：47804500, Web of Science ID：WOS:000277300700029
• Dielectric tunability and electro-optic effect of Ba_0.5Sr_0.5TiO₃ thin films　　　　　　　　　　　　　　　
  K. Takeda; T. Muraishi; T. Hoshina; H. Takeda; T. Tsurumi
  JOURNAL OF APPLIED PHYSICS, Volume：107, Number：7, First page：074105, Apr. 2010, [Reviewed]
  We elucidated the relationship between the dielectric tunability and the electro-optic (EO) effect. A new measurement system for EO effect and dielectric permittivity (epsilon(r)) was developed to investigate the accurate correlation between EO and dielectric properties of epitaxial barium strontium titanate, Ba0.5Sr0.5TiO3 (BST) thin films grown on SrTiO3 (STO) substrates. The BST films had a strained lattice with a large lattice parameter along the thickness direction. Small birefringence was induced in the as-deposited film by the alignment of the c-axis in the film plane. The tunability of dielectric permittivity calculated from the complex voltage and current with planer electrodes reached to 53.1%, and the tunability of birefringence by EO effect was 0.6%. The birefringence change from EO effect was much lower than the tunability of dielectric permittivity. Therefore, there is no strong correlation between the dielectric tunability and EO effect, and the materials with high tunability do not always exhibit high EO effect. Finally, we discussed how to obtain the materials with high EO effect considering these results. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3371679]
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.3371679
  DOI ID：10.1063/1.3371679, ISSN：0021-8979, ORCID：47804490, Web of Science ID：WOS:000276795400064
• Wide Range Dielectric Spectroscopy of Barium Strontium Titanate Ceramics　　　　　　　　　　　　　　　
  Takashi Teranishi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：421-422, First page：273, Last page：276, Jan. 2010, [Reviewed]
  Wide band dielectric spectroscopy was applied from kHz to THz region for the analysis of both the ionic and the dipole polarization in Ba(0.6)Sr(0.4)TiO(3) ceramics. The dielectric permittivity above the dielectric maximum temperature (T(m)) is mostly dominated by the ionic polarization, while that below T(m) is governed by the dipole polarization. Dielectric permittivity given by the dipole polarization increased and the relaxation frequency decreased with decreasing temperature. These phenomena are related to a increase of the size of polar nanoregions (PNRs).
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.421-422.273
  DOI ID：10.4028/www.scientific.net/KEM.421-422.273, ISSN：1013-9826, ORCID：47804508, Web of Science ID：WOS:000279342100064
• Preparation of (Ba_1-x,Sr_x)TiO₃ Thin Films on Glazed Alumina Substrate and Improvement of Temperature Dependence of Dielectric Properties　　　　　　　　　　　　　　　
  Takashi Nozaka; Yoji Mizutani; Gun Bhakdisongkhram; Yuta Kawakami; Masahiro Echizen; Takashi Nishida; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  Key Engineering Materials, Volume：421-422, First page：127, Last page：131, Jan. 2010, [Reviewed]
  In this study, (Ba1-x, Sr-x)TiO3 thin films of various composition ratios were deposited on glazed Al2O3 substrates by the CSD method, and the temperature dependence of the dielectric property was analyzed. The dielectric property of the BST (80/20) thin film annealed at 800 degrees C was highly tunable, and the temperature dependence of the dielectric constant was stabilized at around room temperature. However, this BST (80/20) thin film exhibited intense ferroelectricity. Its tan delta intensified to 0.0511 in the high-frequency range (1 MHz). After the BST thin film was annealed at 600 degrees C, the grain size of the BST thin film was reduced to 40 nm and the ferroelectricity was alleviated. The dielectric constant, tan delta, and tunability of the BST thin film at 100 kHz were 158, 0.0170, and 39.6% (214 kV/cm, 6.0 V), respectively. The change rate of the dielectric constant, which indicates its temperature dependence, was +/- 7% or less in the range of -55 to 85 degrees C. Therefore, this BST thin film was considered to guarantee a wide operation temperature range for microwave tunable devices.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.421-422.127
  DOI ID：10.4028/www.scientific.net/KEM.421-422.127, ISSN：1013-9826, ORCID：47804503, Web of Science ID：WOS:000279342100030
• Fabrication of Dielectric/Conductive Hybrid Artificial Superlattices using Molecular Beam Epitaxy Method　　　　　　　　　　　　　　　
  Yu Yonezawa; Hiroyuki Kinbara; Hiroki Umehara; Hirofumi Kakemoto; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：421-422, First page：139, Last page：142, Jan. 2010, [Reviewed]
  Artificial super-lattices of (4) (BTO(10)/STO(10)) were fabricated on STO(001) substrate by the molecular beam epitaxy method (MBE), and the molecular layers of SrRuO(3)(SRO) was introduced into these superlattices as conductive layers. The superlattices introduced two conductive layers showed the enormous dielectric permittivity. On the other hand, the permittivity of the superlattice introduced one conductive layer was almost same as that of BTO(10)/STO(10). In the case of introducing two conductive layers, the moving electrons between two layers induced the interfacial polarization. Especially, the superlattice with two SRO conductive layers, the distance between these layers in a superlattice is 18 molecular layers, showed the highest relaxation frequency 132 kHz and biggest capacitance.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.421-422.139
  DOI ID：10.4028/www.scientific.net/KEM.421-422.139, ISSN：1013-9826, ORCID：47804497, Web of Science ID：WOS:000279342100033
• Fabrication of PbTiO₃ Nanocrystals on Atomically Flat Sapphire Substrates by Sputtering　　　　　　　　　　　　　　　
  Takashi Nishida; Koichi Kubo; Masahiro Echizen; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  Key Engineering Materials, Volume：421-422, First page：502, Last page：505, Jan. 2010, [Reviewed]
  In order to perform the growth position control, PbTiO3 (x=0) (PTO) nanocrystals were deposited on atomically flat and non-atomically flat alpha-Al2O3 substrates by RF magnetron sputtering. The atomically flat substrates with atomic steps and terrace are expected to induce the lateral growth along a terrace between the surface steps. In the case of the atomically flat, the nanocrystals got lined up along the atomic steps, and uniform nanocrystals were obtained on surface in same pitch.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.421-422.502
  DOI ID：10.4028/www.scientific.net/KEM.421-422.502, ISSN：1013-9826, ORCID：47804498, Web of Science ID：WOS:000279342100117
• Fabrication and positive temperature coefficient of resistivity properties of semiconducting ceramics based on the BaTiO₃-(Bi_1/2K_1/2)TiO₃ system　　　　　　　　　　　　　　　
  H. Takeda; H. Harinaka; T. Shiosaki; M. A. Zubair; C. Leach; R. Freer; T. Hoshina; T. Tsurumi
  JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Volume：30, Number：2, First page：555, Last page：559, Jan. 2010, [Reviewed], [Lead, Corresponding]
  BaTiO3-(Bi1/2K1/2)TiO3 (BT-BKT) ceramics have a low rho(RT) of 10(1)-10(2) Omega cm like that of semiconducting materials prepared by sintering in a N-2 flow with low O-2 concentration. By annealing in air, the BT-BKT ceramics show an abrupt increase in their resistivity near the T-c, namely, a positive temperature coefficient of resistivity (PTC) characteristic. With 5 mol% and 10 mol% BKT added to BT, the ceramics display the PTC characteristic at 155 degrees C and 165 degrees C, respectively. Furthermore, the ratio, rho(max)/rho(RT), of the highest resistivity (rho(max)) and the resistivity at room temperature (rho(RT)) of the ceramics increased on adding a small amount of Mn and a sintering aid. (C) 2009 Elsevier Ltd. All rights reserved.
  ELSEVIER SCI LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jeurceramsoc.2009.08.009
  DOI ID：10.1016/j.jeurceramsoc.2009.08.009, ISSN：0955-2219, ORCID：47804496, Web of Science ID：WOS:000272455600076
• Effects of Pretreatments on deposition rate of Films in Aerosol Deposition Method　　　　　　　　　　　　　　　
  Kensuke Mihara; Takuya Hoshina; Hirofumi Kakemoto; Hiroaki Takeda; Takaaki Tsurumi
  Key Engineering Materials, Volume：421-422, First page：165, Last page：168, Jan. 2010, [Reviewed]
  In the aerosol deposition method (ADM), we investigated an influence of pre-treatments for barium titanate powders as raw material on the deposition rate of thick films. By sieving and drying the powder, deposition rate of the films fabricated by ADM was effectively enhanced. On the other hand, heating the powders at 400-800 degrees C, the resulting powders caused low deposition rate of the films. When a planetary milling was performed prior to charge aerosol chamber, the deposition rate of the films was four times higher than that in deposition using the powder without milling. By changing the milling rotation rate, we control size of agglomerated particles consisting of powders, which results in the control of deposition rate of the films.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.421-422.165
  DOI ID：10.4028/www.scientific.net/KEM.421-422.165, ISSN：1013-9826, ORCID：47804494, Web of Science ID：WOS:000279342100039
• Miniature Ultrasonic Motor Using Shear Mode of Potassium Sodium Niobate-Based Lead-Free Piezoelectric Ceramics　　　　　　　　　　　　　　　
  Enzhu Li; Ryo Sasaki; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：48, Number：9, First page：09KD11, Sep. 2009, [Reviewed], [Corresponding]
  A miniature piezoelectric ultrasonic motor (USM) using the shear mode of (K,Na)NbO(3) (KNN)-based lead-free piezoelectric ceramics was developed. The motor can be driven in the shearing and bending vibration modes. By using the finite-element method, the motor vibration modes and driving mechanism were modeled. Both the "soft-type" (high-d USM) and "hard-type" (high-Q(m) USM) KNN-based lead-free piezoelectric ceramics were employed to clarify the characteristics of USMs. The experimental results reveal that the high-d USM widens the band of operational frequency in both vibration modes. In the shearing vibration mode, the high-d USM showed a revolution speed of 416 rpm, a torque of 41.5 mu N m, and an efficiency of 0.6%, whereas the high-Q(m) USM showed the same characteristics of 313 rpm, 19.6 mu N m and 1.6%, respectively. In the bending vibration mode, the characteristics of the high-Q(m) USM were 376 rpm, 51.4 mu N m and 0.4%; however, the characters of the high-d USM deteriorated owing to the shift in resonance frequency caused by heat generation. (C) 2009 The Japan Society of Applied Physics
  JAPAN SOCIETY APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.48.09KD11
  DOI ID：10.1143/JJAP.48.09KD11, ISSN：0021-4922, ORCID：47804516, Web of Science ID：WOS:000270564800049
• Domain Contribution to Dielectric Properties of Fine-Grained BaTiO₃ Ceramics　　　　　　　　　　　　　　　
  Takuya Hoshina; Yoichi Kigoshi; Saki Hatta; Hiroaki Takeda; Takaaki Tsurumi
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：48, Number：9, First page：09KC01, Sep. 2009, [Reviewed]
  Pure BaTiO3 ceramics with various grain sizes were prepared by a conventional sintering method, a two-step sintering method, and a rate-controlled two-step sintering method. The permittivity of the ceramics increased with decreasing grain size when the grain size was more than 1.1 mu m, while that decreased when the grain size was below 1 mu m. Field emission scanning electron microscopy (FE-SEM) observations revealed that most of the domains in BaTiO3 grains had simple lamellar structures, and 90 degrees domain width decreased with decreasing grain size. By ultrawide range dielectric spectroscopy, the domain contribution to the permittivity was investigated. For the BaTiO3 ceramics with grain sizes over 1 mu m, the dipole and ionic polarizabilities were enhanced by the high domain density. In contrast, for the BaTiO3 ceramics with grain sizes below 1 mu m, these polarizabilities were weakened. (C) 2009 The Japan Society of Applied Physics
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.48.09KC01
  DOI ID：10.1143/JJAP.48.09KC01, ISSN：0021-4922, ORCID：47804513, Web of Science ID：WOS:000270564800028
• Size Effect of Barium Titanate and Computer-Aided Design of Multilayered Ceramic Capacitors　　　　　　　　　　　　　　　
  Takaaki Tsurumi; Takuya Hoshina; Hiroaki Takeda; Youichi Mizuno; Hirokazu Chazono
  IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Volume：56, Number：8, First page：1513, Last page：1522, Aug. 2009, [Reviewed]
  The size effect of BaTiO(3) (BTO) is the most important issue to design multilayer ceramic capacitors (MLCCs) with high capacitance. In the size effect of BTO particles, the size dependence of dielectric permittivity related with the complex structure in BTO nano-particles. The grain size dependence of dielectric permittivity in BTO ceramics was due to the domain wall contribution. The core-shell structure played an important role in the size effect of dielectric layers in X7R-MLCCs. Computer simulation technique was developed to predict the limit of capacitance density of MLCCs produced by the current technology. Dielectric properties of MLCCs with different particle size of BTO were measured, and the data were analyzed using B-SPLINE fitting to predict dielectric permittivity kit arbitrary temperatures and AC-fields. The dielectric properties of barium titanate grains smaller than 100 nm were predicted using least squares fitting of the B-SPLINE coefficients. It was found from the simulation that the use of barium titanate grains smaller than 80 nm did not give all advantage to increase the capacitance density as well as temperature stability of the MLCCs. The maximum capacitance was predicted for the 1608 (mm) chip size.
  IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, English, Scientific journal
  DOI：https://doi.org/10.1109/TUFFC.2009.1214
  DOI ID：10.1109/TUFFC.2009.1214, ISSN：0885-3010, eISSN：1525-8955, ORCID：47804519, Web of Science ID：WOS:000268553100003
• Controlling factors of film-thickness in improved aerosol deposition method　　　　　　　　　　　　　　　
  Kensuke Mihara; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：117, Number：1368, First page：868, Last page：872, Aug. 2009, [Reviewed]
  To understand the controlling factor of film thickness in aerosol deposition method (ADM), the deposition apparatus was improved at first and the effect of pretreatment of raw barium titanate powder was studied. A developed aerosol generator where the carrier gas was separated from the aerosol generating gas was effective to avoid the agglomeration of powders during the deposition. Two dimensional scanning of the substrate decreased the film-thickness distribution caused by the imhomogeneity of deposition rate in a line-type nozzle. Effect of pretreatments of raw powders, including sieving, drying, planetary ball milling and heating was examined, respectively. There was an optimum rotational velocity of planetary milling to increase the film thickness, indicating that adequate agglomeration of raw powders enhance the film deposition. The film thickness decreased as the heating temperature increased. The heating strengthened the agglomeration of raw powders which restricted the film deposition because the kinetic energy of particles in the aerosol was consumed to break the agglomerations rather than making film. Weakly agglomerated powders with optimum size enhanced the film thickness in ADM. (C)2009 The Ceramic Society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.117.868
  DOI ID：10.2109/jcersj2.117.868, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804510, Web of Science ID：WOS:000268981400003
• Ultrawideband dielectric spectroscopy of BaZr_xTi_1-xO₃ ceramics and its microscopic mechanism of polarization　　　　　　　　　　　　　　　
  Takashi Teranishi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF APPLIED PHYSICS, Volume：105, Number：11, First page：114102, Jun. 2009, [Reviewed]
  Ultrawideband dielectric spectroscopy analysis of barium zirconate titanate (BaZrxTi1-xO3, BZT) ceramics at different temperatures disclosed the contribution of both the dipole and the ionic polarizations to permittivity at around dielectric maximum temperature (T-m). In BaZr0.25Ti0.75O3 ceramics, the permittivity around Tm is dominated by the temperature dependence of the permittivity determined by the dipole polarization (epsilon(dipole)). In relaxor ferroelectrics, the diffuse dielectric response around Tm could be derived from the temperature dependence of epsilon(dipole). The variation of epsilon(dipole) with temperature could be also explained by the growth process of polar nanoregions (PNRs) and the damping process of the thermal fluctuation of dipoles in PNRs. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3131624]
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.3131624
  DOI ID：10.1063/1.3131624, ISSN：0021-8979, ORCID：47804520, Web of Science ID：WOS:000267053200111
• Polarization behavior in diffuse phase transition of Ba_xSr_1-xTiO₃ ceramics　　　　　　　　　　　　　　　
  Takashi Teranishi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  JOURNAL OF APPLIED PHYSICS, Volume：105, Number：5, First page：054111, Mar. 2009, [Reviewed]
  Ultrawide band dielectric spectroscopy analysis of barium strontium titanate [BaxSr1-xTiO3 (BST)] ceramics at different temperatures disclosed a contribution of the dipole and the ionic polarizations to their diffuse phase transition (DPT). In the BST ceramics, thermal behavior of the ionic polarization governs the DPT. The dielectric maximum temperature (T-m) is in agreement with the maximum temperature of the permittivity determined by the ionic polarization. The maximum of the permittivity determined by the ionic polarization at the T-m is caused from the decrement of the vibration frequency of the soft mode. The dipole polarization gives small contribution to the DPT. The gradual increase in the permittivity determined by the dipole polarization with decreasing temperature could be explained by the increase in the size of the polar nanoregions.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.3089250
  DOI ID：10.1063/1.3089250, ISSN：0021-8979, eISSN：1089-7550, ORCID：47804517, Web of Science ID：WOS:000264156300079
• Fabrication of PbTiO₃ Nanocrystals on Atomically Flat Sapphire Substrates by RF Magnetron Sputtering　　　　　　　　　　　　　　　
  Takashi Nishida; Koichi Kubo; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  FERROELECTRICS, Volume：381, Number：1 PART 2, First page：74, Last page：79, Mar. 2009, [Reviewed]
  Recently, there has been great interest in nanosized ferroelectric materials because of the need to produce higher capacity ferroelectric memory devices. Since the characteristics of these memory devices are affected by the dielectric behavior in nanoregions, it is important to produce nanocrystals that are highly uniform both in terms of size and quality. Nanocrystals have been prepared by bottom-up methods, such as initial growth nucleation; however, it is difficult to control growth position and crystal size in these methods. In this study, lead titanate (PbTiO3) nanocrystals were prepared on atomically flat sapphire substrates at a very low deposition rate in order to achieve position and size control. Atomically flat surfaces of sapphire (0001) were formed by annealing at 1000 degrees C and they had a step-terrace structure with a step height of 0.22 nm and a terrace width of 70 nm. A shield plate for reducing the deposition rate was placed in front of the substrate during sputtering. Nanocrystals with a uniform size of about 30 nm were successfully grown on the step-edge of the surface, demonstrating that it is possible to fabricate well-ordered nanocrystal arrays using our shielding technique. The crystals obtained were evaluated by X-ray photoluminescence and Raman spectroscopy, and the results revealed that perovskite PbTiO3 nanocrystals had been produced.
  TAYLOR & FRANCIS LTD, English, Scientific journal
  DOI：https://doi.org/10.1080/00150190902869681
  DOI ID：10.1080/00150190902869681, ISSN：0015-0193, ORCID：47804515, Web of Science ID：WOS:000269689400011
• Dielectric, piezoelectric, and electromechanical phenomena in (K_0.5Na_0.5)NbO₃-LiNbO₃-BiFeO₃-SrTiO₃ ceramics　　　　　　　　　　　　　　　
  Enzhu Li; Ryo Suzuki; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  APPLIED PHYSICS LETTERS, Volume：94, Number：13, First page：132903, Mar. 2009, [Reviewed]
  The effect of the substitutions of BiFeO3 (BF) and SrTiO3 (ST) to (Na0.5K0.5)NbO3-LiNbO3 (KNN-LN) ceramics was studied as a candidate of lead-free piezoceramics. The piezoelectric property is enhanced near the phase transition composition caused by the distortion of crystal lattice by Li+ and also the strong ferroelectric nature of BF. The ST was found to be effective in improving the temperature dependence of the KNN ceramics. Small amount of ST also promoted the incorporation of LN and BF into the crystal lattice, and enhanced the piezoelectric performance furthermore. The 94.5(Na0.5K0.5)NbO3-4.5LiNbO(3)-0.5SrTiO(3)-0.5BiFeO(3) ceramics showed excellent piezoelectric properties of d(15)=231 pC/N, d(33)=155 pC/N, and d(31)=70 pC/N.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.3112564
  DOI ID：10.1063/1.3112564, ISSN：0003-6951, ORCID：47804512, Web of Science ID：WOS:000264888500040
• Fabrication and operation limit of lead-free PTCR ceramics using BaTiO₃-(Bi_1/2Na_1/2)TiO₃ system　　　　　　　　　　　　　　　
  Hiroaki Takeda; Takeshi Shimada; Yoshiaki Katsuyama; Tadashi Shiosaki
  JOURNAL OF ELECTROCERAMICS, Volume：22, Number：1-3, First page：263, Last page：269, Feb. 2009, [Reviewed], [Lead, Corresponding]
  The electric properties of BaTiO3-(Bi1/2Na1/2)TiO3 (BT-BNT) solid solution ceramics were studied as a lead-free PTCR (positive temperature coefficient of resistivity) thermistor material usable over 130A degrees C. For determining the maximum switching temperature T (s), the phase diagram of BT-BNT binary system was clarified. Two semiconductorization processes and their electric properties are described. The lanthanum(La)-doped BBNT ceramics sintered in air still showed dielectric behaviors, but the niobium(Nb)-doped ones had a low resistivity at room temperature, rho (RT), on the order of 10(3) Omega cm and showed a PTC behavior. Sintering under a low O-2 atmosphere produces BT-BNT ceramics with less than 10(2) Omega cm compared to those prepared in air. Our current research produced the BBNT ceramics with T (s) values around 210A degrees C by increasing the (Bi1/2Na1/2) content in the ceramics.
  SPRINGER, English, Scientific journal
  DOI：https://doi.org/10.1007/s10832-007-9398-6
  DOI ID：10.1007/s10832-007-9398-6, ISSN：1385-3449, ORCID：47804514, Web of Science ID：WOS:000263498800045
• Preparation of (Ba, Sr)TiO₃ Thin Films on Glazed Alumina Substrate and Analysis of Their Electric Properties　　　　　　　　　　　　　　　
  Takashi Nozaka; Yoji Mizutani; Bhakdisonakhram Gun; Takuya Tsuchikawa
  Key Engineering Materials, Volume：388, First page：191, Last page：194, Jan. 2009, [Reviewed]
  The (Ba0.6Sr0.4)TiO3 (BST) thin films were formed on a Pt bottom electrode/glazed-Al2O3 substrates by a chemical Solution deposition (CSD) method, The BST films were annealed at temperatures between 600 and 800 degrees C in a rapid thermal annealing (RTA) process and grown at each temperature with a random orientation. The grain size of the BST films enlarged and the electrical properties of the BST films improved as the annealing temperature rose. The grain size of the film annealed at 800 degrees C enlarged to be 80 nm. The averaged surface roughness Ra was 2.927 nm, which resulted in a favorable degree of planarity. The dielectric constant and loss tangent of the film at I MHz were 403 and 0.049, respectively. The film also displayed a high degree of tunability, which was 58.3% (at 429 kV/cm). These results indicated that high-quality BST thin films could be formed on an extremely cheap glazed-Al2O3 substrates.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.388.191
  DOI ID：10.4028/www.scientific.net/KEM.388.191, ISSN：1013-9826, ORCID：47804518, Web of Science ID：WOS:000263263800046
• Dielectric, elastic and piezoelectric properties of RCa₄O(BO₃)₃ (R = rare-earth elements) crystals with monoclinic structure of point group m　　　　　　　　　　　　　　　
  Hiroyuki Shimizu; Takashi Nishida; Hiroaki Takeda; Tadashi Shiosaki
  JOURNAL OF CRYSTAL GROWTH, Volume：311, Number：3, First page：916, Last page：920, Jan. 2009, [Reviewed]
  Rare-earth calcium oxoborate RCa4O(BO3)(3) (R = La, Gd, Y) piezoelectric single crystals were successfully grown by a conventional RF-heating Czochralski (Cz) technique. They belong to the monoclinic system with point group m, and have 27 independent material constants. We developed the determination scheme (cuts and vibration modes) of the material constants in point group m. Their material constants were evaluated on the basis of the determination scheme and systematically compared. Also, the Rayleigh surface acoustic wave (RSAW) velocities v and coupling factors K-2 for the fundamental X-, Y- and Z-cuts were theoretically simulated in their crystals by Campbell and Jones's method, which showed a good agreement with the measured values. Moreover, from the calculated result in their all propagation direction, it was confirmed that (180 degrees, 120 degrees, 167 degrees)-cut of the RCa4O(BO3)(3) (R = Y) and (180 degrees, 146 degrees, 167 degrees)-cut of the RCa4O(BO3)(3) (R = La), indicated excellent RSAW propagation properties when compared with existing piezoelectric crystals. (C) 2008 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jcrysgro.2008.09.144
  DOI ID：10.1016/j.jcrysgro.2008.09.144, ISSN：0022-0248, ORCID：47804511, Web of Science ID：WOS:000264161700118
• Analysis of Nonlinear Dielectric Characteristics of (Ba, Sr)TiO₃ Thin Films and Their Frequency Conversion Application　　　　　　　　　　　　　　　
  Takashi Nishida; Takashi Nozaka; Takuya Tsuchikawa; Masahiro Echizen; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  Key Engineering Materials, Volume：388, First page：183, Last page：186, Jan. 2009, [Reviewed]
  (Ba,Sr)TiO(3) (BST) thin films have been investigated because of significant interest in device applications of their nonlinear dielectric properties such as in frequency tunable devices. We have investigated frequency conversion devices using BST films as new nonlinear devices, such as frequency mixers and multipliers. In this paper, we report the evaluation of nonlinear properties of various capacitors, and the experimental equation of the properties and the equivalent circuit model for frequency converters were established. A frequency multiplier using the BST film capacitor was fabricated, and obvious third harmonic signals could be observed. A conversion efficiency of -20 dB was obtained with a low input power of 0.25 W. Analysis of the converter with an equivalent circuit was also carried out, and the calculated output voltage agreed well with the measured result. The model is expected to be used for the analysis and improvement of conversion devices.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/0-87849-359-x.183
  DOI ID：10.4028/0-87849-359-x.183, ISSN：1013-9826, ORCID：47804509, Web of Science ID：WOS:000263263800044
• Heat-cycle endurance and in-plane thermal expansion of Al₂O₃/Al substrates formed by aerosol deposition method　　　　　　　　　　　　　　　
  Ryo Sakamaki; Takuya Hoshina; Hirofumi Kakemoto; Kouichi Yasuda; Hiroaki Takeda; Jun Akedo; Takaaki Tsurumi
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：116, Number：1360, First page：1299, Last page：1303, Dec. 2008, [Reviewed]
  A new heat radiation substrate for high power modules has been proposed by utilizing Al2O3 thick films formed by the aerosol deposition method (ADM) on Al substrates. Dense Al2O3 thick films (AD-Al2O3) could be obtained by the ADM at room temperature. A heat-cycle endurance test between -80 degrees C and 180 degrees C revealed that the AD-Al2O3/Al substrates were superior to the conventional direct brazed aluminum (DBA) substrates using AlN ceramics bounded to Al substrates. No lamination was observed between the AD-Al2O3 films and Al substrates after heat-cycle test in spite of the difference of thermal expansion coefficient between Al2O3 and Al. The in-plane thermal expansion coefficient of AD-Al2O3 films was almost the same as that of Al substrates, indicating that plastic deformation was induced in the AD-Al2O3 films consisting of nano-sized grains to relax the stress caused by the difference of thermal expansion coefficient. (c) 2008 The Ceramic society of Japan. All rights reserved.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj2.116.1299
  DOI ID：10.2109/jcersj2.116.1299, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804527, Web of Science ID：WOS:000261427500010
• Fabrication of lead-free and high T_c BaTiO₃-based thermistor ceramics using deoxidizing effect of oxygen-containing alpha-zirconium　　　　　　　　　　　　　　　
  Hiroaki Takeda; Yoichiro Hoshi; Tsukuru Kinoshita; Toetsu Shishido; Takashi Nishida; Tadashi Shiosaki
  CERAMICS INTERNATIONAL, Volume：34, Number：8, First page：2073, Last page：2077, Dec. 2008, [Reviewed], [Lead, Corresponding]
  Oxygen-containing alpha-zirconium (alpha-ZrOx) has been synthesized by an arc melting method. The oxidation of the alpha-ZrOx powders occurs at 480 degrees C in air. After this oxidation, the reaction product is normal zirconia ZrO2 powders. We demonstrate an application of this oxidation process. By firing green bodies of BaTiO3-(Bi1/2Na1/2)TiO3 solid-solution ceramics in contact with the alpha-ZrOx powders, the ceramics acquire a semi conductivity with a positive temperature coefficient of resistivity (PTC) behavior. We propose a method to prepare lead-free PTC thermistor ceramics with a Curie temperature T, over 130 degrees C, which is that of BaTiO3, in air. (C) 2007 Elsevier Ltd and Techna Group S.r.l All rights reserved.
  ELSEVIER SCI LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.ceramint.2007.08.009
  DOI ID：10.1016/j.ceramint.2007.08.009, ISSN：0272-8842, ORCID：47804525, Web of Science ID：WOS:000260735500042
• Annealing effects on the characteristics of high T_c lead-free barium titanate-based positive temperature coefficient of resistivity ceramics　　　　　　　　　　　　　　　
  Ping-Hua Xiang; Hisashi Harinaka; Hiroaki Takeda; Takashi Nishida; Kiyoshi Uchiyama; Tadashi Shiosaki
  JOURNAL OF APPLIED PHYSICS, Volume：104, Number：9, Nov. 2008, [Reviewed]
  Annealing effects on the positive temperature coefficient of resistivity (PTCR) behavior of (Bi(1/2)Na(1/2))TiO(3) and (Bi(1/2)K(1/2))TiO(3) modified BaTiO(3) semiconducting ceramics are investigated. The annealing treatments result in the occurrence of the PTCR effect and the increased resistivity jump. The impedance spectra reveal that the resistivity of grain interior of annealed sample is little influenced by the annealing process, indicating that the increase in the overall resistivity is entirely a grain-boundary effect. A higher annealing temperature leads to an increase in acceptor state density, potential barrier height and barrier layer width, which contributes to the improved PTCR effect in the annealed samples. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3013447]
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.3013447
  DOI ID：10.1063/1.3013447, ISSN：0021-8979, ORCID：47804521, Web of Science ID：WOS:000260941700094
• Electro-optic anisotropy of epitaxially grown (Pb,La)(Zr,Ti)O₃ films fabricated by modified sol-gel process　　　　　　　　　　　　　　　
  Masahiro Echizen; Takeshi Fujii; Takashi Nozaka; Takashi Nishida; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：47, Number：9, First page：7545, Last page：7548, Sep. 2008, [Reviewed]
  Highly-quality epitaxially grown (Pb,La)(Zr,Ti)O-3 (PLTZ) flms were successfully fabricated on single-crystalline sapphire (012) substrates using a modified sol-gel process. The crystallographic relationship between the PLZT film and the sapphire substrate, and the detailed electro-optic (EO) properties of the films were investigated. Large linear EO coefficients,. as large as 5 10 pm/V. were obtained when an electric field was, applied at 145 angle to the PLZT {110}. In turn, smaller EO coefficients were obtained when an electric field was applied at 0 degrees and 90 degrees angles to PLZT {110}. A strong EO anisotropy was observed according to the configuration of the input light polarization and the applied electric field.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.47.7545
  DOI ID：10.1143/JJAP.47.7545, ISSN：0021-4922, ORCID：47804524, Web of Science ID：WOS:000259657800017
• Effect of interface structure on electrical properties of (Ba,Sr)TiO₃ thin films on glazed alumina substrate　　　　　　　　　　　　　　　
  Takashi Nozaka; Yoji Mizutani; Bhakdisongkhram Gun; Masahiro Echizen; Takashi Nishida; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：47, Number：9, First page：7494, Last page：7499, Sep. 2008, [Reviewed]
  We examined the impact that the electrode/(Ba,Sr)TiO3 (BST) interface structures have on electric properties by investigating the electrical conduction mechanism of the BST thin-film capacitors with Pt and Au top electrode. The BST thin films were prepared on the Pt bottom electrode/glazed Al2O3 substrate by chemical solution deposition (CSD). The dielectric property of the as-deposited Pt/BST/Pt capacitor had it large frequency dispersion and the leakage current properties deteriorated because the Pt top electrode/BST interface structure is rough. However. by post-annealing For 30 min at 400 degrees C after the top electrode Was deposited. the frequency and temperature properties improved. The Schottky barrier height at the Pt top electrode/BST interface was 1.03 eV and that at the Au/BST interface was 0.73 eV, which indicated that its electrical conduction mechanism depends oil the Schottky emission model. The dielectric constant, tan delta, and tunability of the Au/BST/Pt capacitor are 200, 0.0178, and 53.7% (at 214 kV/cm, 6.0 V), respectively, which showed excellent dielectric properties. This suggests that high-quality BST films for application to tunable microwave devices can be formed on a very inexpensive glazed Al2O3 substrate.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.47.7494
  DOI ID：10.1143/JJAP.47.7494, ISSN：0021-4922, ORCID：47804523, Web of Science ID：WOS:000259657800006
• Growth and piezoelectric properties of Al-substituted langasite-type La₃Nb_0.5Ga_5.5O₁₄ crystals　　　　　　　　　　　　　　　
  Hiroaki Takeda; Tomoaki Kuze; Takashi Nishida; Kiyoshi Uchiyama; Tadashi Shiosaki
  MATERIALS RESEARCH BULLETIN, Volume：43, Number：7, First page：1731, Last page：1736, Jul. 2008, [Reviewed], [Lead, Corresponding]
  The influences of aluminum substitution for gallium in the langasite-type La3Nb0.5Ga5.5O14 (LNG) crystals on their growth and electric properties were investigated. Al-substituted LNG (La3Nb0.5Ga5.5-x,AlxO14; LNGAx) single crystals up to the solubility limit x = 0.2 have been grown by the conventional Czochralski technique. The electric properties of the LNGAx crystals were investigated and compared to those of LNG. With Al substitution, the piezoelectric constants, d(11) and d(14), were slightly higher. The LNGAx crystals showed a temperature dependence of d(11) similar to that of the LNG crystal. (c) 2007 Elsevier Ltd. All rights reserved.
  PERGAMON-ELSEVIER SCIENCE LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.materresbull.2007.07.029
  DOI ID：10.1016/j.materresbull.2007.07.029, ISSN：0025-5408, ORCID：47804526, Web of Science ID：WOS:000257365900014
• X-ray topography of piezoelectric La₃Ta_0.5Ga_5.5O₁₄ crystal grown by czochralski method　　　　　　　　　　　　　　　
  Yasuhiro Yoneda; Jun'ichiro Mizuki; Hiroaki Takeda; Tadashi Shiosaki
  IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Volume：55, Number：5, First page：971, Last page：974, May 2008, [Reviewed]
  We performed synchrotron X-ray topography on a La3Ta0.5Ga5.5O14 (LTG) crystal grown by the Czochralski method. Since a synchrotron X-ray source can provide high-energy X-rays, one can detect bulk structures by X-ray topography. LTG is one of the most attractive piezoelectric crystals along with La3Ga5SiO14 (LGS) because of its excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from a stoichiometric melt, it was expected that single crystals with better quality than the LGS crystal, which cannot be grown from a stoichiometric system but only from a congruent melt, can be obtained. However, 60 keV X-ray topography revealed that the LTG crystal quality was not as high as the LGS crystal quality. The crystal quality of the central region was lower than that of the surrounding region.
  IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, English, Scientific journal
  DOI：https://doi.org/10.1109/TUFFC.2008.741
  DOI ID：10.1109/TUFFC.2008.741, ISSN：0885-3010, ORCID：47804529, Web of Science ID：WOS:000255537600007
• Polar laser dyes dispersed in polymer matrices: Reverification of charge transfer character and new optical functions　　　　　　　　　　　　　　　
  Giseop Kwak; Chisato Okada; Michiya Fujiki; Hiroaki Takeda; Takashi Nishida; Tadashi Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS, Volume：47, Number：3, First page：1753, Last page：1756, Mar. 2008, [Reviewed]
  In this paper, we describe the photophysical properties and new functions of 4-(dicyanomethylene)-2-methyl-6-(p-dimethyla-minostyryt)-4H-pyran (DCM) and its derivative, 2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-9-yl)-ethen-yl]-4H-pyran-4-ylidene)propane dinitrile (DCM2) in various polymer matrices, with respect to intramolecular charge transfer (ICT). The maximum fluorescence wavelengths of DCM and DCM2 shifted to red with an increase in the dielectric constant of the polymer matrix. The fluorescence lifetime shortened according to the matrix polarity. When a polymer with a dielectric constant varying according to its crystalline structure, poly (vinylidenefluoride-co-trifluoroethylene) (PVdF-co-TrFE), was used as a matrix, we were able to thermally tune the fluorescence wavelength as well as the fluorescence intensity of DCM2. The locked molecular structure of DCM2 was very effective for maintaining the charge transfer character during thermal stimulation.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.47.1753
  DOI ID：10.1143/JJAP.47.1753, ISSN：0021-4922, ORCID：47804528, Web of Science ID：WOS:000255020100067
• Characterization of manganese-doped BaTiO₃-(Bi_1/2Na_1/2)TiO₃ positive temperature coefficient of resistivity ceramics using impedance spectroscopy　　　　　　　　　　　　　　　
  Ping-Hua Xiang; Hiroaki Takeda; Tadashi Shiosaki
  JOURNAL OF APPLIED PHYSICS, Volume：103, Number：6, Mar. 2008, [Reviewed]
  Small amount of manganese ( Mn )- doped BaTiO(3) - (Bi(1/2)Na(1/2)) TiO(3) ( BT-BNT ) positive temperature coefficient of resistivity ceramics are investigated by impedance analyses. The impedance/ modulus spectroscopic plots reveal that a third resistance- capacitance ( RC ) response besides grains and grain boundaries is exhibited in the Mn-free BT-BNT ceramic with 4 mol % BNT, but is not observed in the Mn- doped samples. The third RC element can be attributed to a barium vacancy- rich layer in the outer grain region. The evidence of impedance spectroscopy indicates that the highly Bi donor is partially compensated by the Mn acceptor and the predominant charge compensation defect shifts from barium vacancies to electrons with doping small amount of Mn dopant. (C) 2008 American Institute of Physics.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.2884714
  DOI ID：10.1063/1.2884714, ISSN：0021-8979, ORCID：47804522, Web of Science ID：WOS:000254536900088
• Synthesis and characterization of PbTiO₃ Ferroelectric nanocrystals on atomically flat a-Al₂O₃ (0001) substrates by RE magnetron sputtering　　　　　　　　　　　　　　　
  Koichi Kubo; Masahiro Echizen; Takashi Nishida; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  Transactions of the Materials Research Society of Japan, Volume：33, Number：1, First page：69, Last page：72, Jan. 2008, [Reviewed]
  PbTiO3 (PTO) ferroelectric nanocrystals were deposited on atomically flat alpha-Al2O3 (0001) substrates by RF magnetron sputtering. The atomically flat alpha-Al2O3 (0001) substrates were obtained by annealing the alpha-Al2O3 (0001) substrate for about 3 hours at 1000-1200 degrees C and the surface with atomic steps and terrace was observed by atomic force microscopy (AFM). In the RF magnetron sputtering method, high energy particles were sputtered on the substrates. Therefore, nucleation of crystals is stimulated at the atomic steps by control particles sputtered with high energy. Their particles were controlled by setting a cover material (alpha-Al2O3) on the substrates. Judging from the result of observations with XRD, XRF and AFM, the crystallized PTO nanocrystals were triangular in shape, with side length of 100-150nm and height of 20-30nm. In addition, it was confirmed by AFM that, when the cover allowed Sputtered particles to approach ascending atomic steps, PTO nanocrystals fell into alignment along the atomic steps. So, it was found that relation between direction of steps and direction in which sputtered particles came flying were very important.
  MATERIALS RESEARCH SOCIETY JAPAN-MRS-J, English, International conference proceedings
  DOI：https://doi.org/10.14723/tmrsj.33.69
  DOI ID：10.14723/tmrsj.33.69, ORCID：49173950, Web of Science ID：WOS:000263875700017
• Structural and Electric Properties of (Ba, Sr)TiO₃ Thin Films on Glazed Alumina Substrate　　　　　　　　　　　　　　　
  Takashi Nozaka; Takashi Nishida; Yoji Mizutani; Bhakdisongkhram Gun; Takuya Tsuchikawa; Masahiro Echizen; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  Transactions of the Materials Research Society of Japan, Volume：33, Number：1, First page：65, Last page：68, Jan. 2008, [Reviewed]
  In this study, we investigated the crystal structure of polycrystalline BST films deposited on the glazed-Al(2)O(3) and alpha-Al(2)O(3) substrates and its electrical properties. The BST films were prepared on the Pt bottom electrode/substrates by the chemical solution deposition (CSD) method. The BST films annealed at 800 degrees C using rapid thermal annealing (RTA) were grown in random orientation on each substrate. The grain sizes were 80 nm and the average surface roughnesses Ra were approximately 3.0 nm. The dielectric constant, tan delta and tunability (at 428 kV/cm) of the Pt/BST/Pt/alpha-Al(2)O(3) film were 476, 0.0321 and 68.6% respectively, and the Pt/BST/Pt/glazed-Al(2)O(3) film also showed practical figures, 429, 0.0498 and 58.3% respectively. We confirmed that the tunability of the Pt/BST/Pt/glazed-Al(2)O(3) film can be maintained at above 50% up to an environmental temperature of around 80 degrees C. This suggests that high quality BST films to apply on tunable microwave devices can be formed on a very inexpensive glazed-Al(2)O(3) substrate.
  MATERIALS RESEARCH SOCIETY JAPAN-MRS-J, English, International conference proceedings
  DOI：https://doi.org/10.14723/tmrsj.33.65
  DOI ID：10.14723/tmrsj.33.65, ORCID：49173949, Web of Science ID：WOS:000263875700016
• Influence of Light Irradiation on Electrical Properties of Lead Zirconate Titanate Film Capacitors　　　　　　　　　　　　　　　
  Takashi Nishida; Takashi Nozaka; Masahiro Echizen; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  Transactions of the Materials Research Society of Japan, Volume：33, Number：1, First page：61, Last page：64, Jan. 2008, [Reviewed]
  Pb(Zr,Ti)O(3) (PZT) thin film capacitors have been widely investigated, due to their various applications, including ferroelectric memories and micro-electromechanical systems. However, degradation of electrical properties of the films is caused by crystal defects, and the exact mechanism for this has not been fully elucidated. We have attempted to investigate defects in the films by thermally stimulated current (TSC) measurements, and the identification of the observed TSC peaks and the relationships between the degradation and TSC signal. However, the behavior of carriers in the films, such as recombination, has not been fully elucidated, and quantitative evaluation of carrier movement and defect density has been difficult. We have therefore investigated the influence of UV-light irradiation on electrical properties of PZT film capacitors.
  The leakage current and capacitance measurements under UV light (lambda = 250 nm) irradiation were carried out. The current and capacitance were gradually changed by the irradiation, revealing that the relaxation time and lifetime of carriers in the films were sufficiently high, above 100 s, and the decrease in the observed current in TSC by recombination seems to be small. The relaxation time slightly decreased with increasing temperature and applied voltage because of carrier drift. The drift properties were also discussed.
  MATERIALS RESEARCH SOCIETY JAPAN-MRS-J, English, International conference proceedings
  DOI：https://doi.org/10.14723/tmrsj.33.61
  DOI ID：10.14723/tmrsj.33.61, ORCID：49173918, Web of Science ID：WOS:000263875700015
• Syntheisis and characterization of bismuth tungstate crystals by solution growth technique　　　　　　　　　　　　　　　
  Masaya Nishida; Hiroaki Takeda; Takashi Nishida; Tadashi Shiosaki
  Key Engineering Materials, Volume：350, First page：81, Last page：84, Oct. 2007, [Reviewed], [Corresponding]
  Growth of ferroelectric Bi2WO6 (BWO) mono-domain bulk crystals was attempted by the vertical-Bridgman (VB) method below the phase transition (ferro- to paraelectric) temperature of 940 degrees C using Li2B4O7 as a flux. In this method, Pt crucibles with different shapes were used. The crucible with a wedged tip bottom produced BWO crystal with a thickness of over 4 mm along the crystallographic c-axis (perpendicular to the spontaneous polarization axis). Using BWO mono-domain crystals grown by slow cooling technique, on the other hand, their electric properties were characterized. The dielectric constants, epsilon(ij), and electromechanical coupling factor, k(33), of the crystals were 70-100 and 36% at room temperature, respectively.
  TRANS TECH PUBLICATIONS LTD, English, International conference proceedings
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.350.81
  DOI ID：10.4028/www.scientific.net/KEM.350.81, ISSN：1013-9826, ORCID：47804535, Web of Science ID：WOS:000250782100020
• Preparation of (Pb,La)(Zr,Ti)O₃ epitaxial thin films by modified sol-gel method and their crystallinity evaluation　　　　　　　　　　　　　　　
  Masahiro Echizen; Takashi Nishida; Takashi Nozaka; Hiroaki Takeda; Kiyoshi Uchiyama; Tadashi Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：46, Number：10B, First page：6933, Last page：6937, Oct. 2007, [Reviewed]
  The preparation of (Pb,La)(Zr,Ti)O-3 (PLZT) films has been widely investigated because of the expectation for their application to high-performance optical devices. We, prepared PLZT films on sapphire substrates by a newly developed modified sol-gel process with methanol, and the crystalline and optical evaluations of the films were performed in detail. In particular, relationships between the modified process and crystallinity were discussed. The crystalline orientation of the films obtained by our modified process was noticeably improved without enlargement of grain size. Thus, optical loss in the films also decreased by 15% using the modified process. In order to investigate crystal growth using the modified process, the observation of the surface state of sapphire by X-ray photoelectron spectroscopy (XPS) was performed. The At 2p on the XPS profile from the surface of the sapphire substrate was removed by surface treatment. It was found that the surface modification with organic molecules was caused by the methanol process. From the results, the effectiveness of modification treatments for the preparation of high-quality PUT films was revealed.
  INST PURE APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.46.6933
  DOI ID：10.1143/JJAP.46.6933, ISSN：0021-4922, ORCID：47804534, Web of Science ID：WOS:000250790200006
• Positive temperature coefficient of resistivity effect of semiconducting BaTiO₃-(Bi_1/2Na_1/2)TiO₃ ceramics prepared by a wet-chemistry route　　　　　　　　　　　　　　　
  Ping-Hua Xiang; Hiroaki Takeda; Tadashi Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：46, Number：10B, First page：6995, Last page：6998, Oct. 2007, [Reviewed]
  Without any additional donor dopants, BaTiO3-(Bi1/2Na1/2)TiO3 (BT-BNT) positive temperature coefficient of resistivity (PTCR) ceramics were successfully prepared by a wet-chemistry route. With 2 mol % BNT addition, the obtained BT-BNT ceramics had semiconductivity and exhibited a PTCR behavior at about 155 degrees C. The onset temperature of the PTCR effect increased to similar to 165 degrees C for the 4 mol % BNT added samples. Room-temperature resistivity rho RT increased with the content of BNT added and the ceramics changed from a semiconductor to an insulator, which was consistent with the variation of the microstructure. The temperature of resistivity anomaly in BT-BNT ceramics also increased with increasing BNT content. A small amount of manganese (Mn) dopant was found to improve the PTCR effect in the BT-BNT system. The possible mechanism underlying the PTCR effect in BT-BNT ceramics was proposed.
  INST PURE APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.46.6995
  DOI ID：10.1143/JJAP.46.6995, ISSN：0021-4922, ORCID：47804533, Web of Science ID：WOS:000250790200020
• High T_c lead-free BaTiO₃-(Bi_1/2Na_1/2)TiO₃ positive temperature coefficient of resistivity ceramics with electrically heterogeneous structure　　　　　　　　　　　　　　　
  Ping-Hua Xiang; Hiroaki Takeda; Tadashi Shiosaki
  APPLIED PHYSICS LETTERS, Volume：91, Number：16, First page：162904, Oct. 2007, [Reviewed]
  A distinct positive temperature coefficient of resistivity effect has been observed in BaTiO3-(Bi1/ 2Na1/ 2) TiO3 (BT- BNT) ceramics sintered in a N-2 flow with low O-2 concentration. With the addition of BNT, the samples exhibit resistivity jumps of 10(3)-10(5) starting at 190 -210 degrees C. X-ray diffraction results indicate that the BNT phase and BT phase formed a solid solution during sintering. An electrically heterogeneous structure, consisting of the grain interiors, outer grain shells, and grain boundaries, is revealed by the complex impedance analyses. The observed dc resistivity jump is attributed to the rapid resistivity rise in both grain boundaries and grain shells. (C) 2007 American Institute of Physics.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.2799878
  DOI ID：10.1063/1.2799878, ISSN：0003-6951, ORCID：47804531, Web of Science ID：WOS:000250295700060
• Difference between local and average. structures of La₃Ga₅SiO₁₄ crystal　　　　　　　　　　　　　　　
  Yasuhiro Yoneda; Hiroaki Takeda; Tadashi Shiosaki; Jun'ichiro Mizuki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：46, Number：10B, First page：7163, Last page：7166, Oct. 2007, [Reviewed]
  The langasite (La3Ga5SiO14, LGS) crystal grown by the Czochralski technique was investigated by X-ray diffraction measurements. The X-ray diffraction profiles of the LGS consisted of sharp Bragg peaks and large amounts of diffuse scatterings. The diffuse scatterings indicated the existence of a local structure, which is different from the average structure of LGS. The local structure was analyzed by the pair-distribution function method. The local structure fluctuated owing to the local disordering of La atoms.
  INST PURE APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.46.7163
  DOI ID：10.1143/JJAP.46.7163, ISSN：0021-4922, ORCID：47804530, Web of Science ID：WOS:000250790200059
• Lead free PTCR ceramics and its electrical properties　　　　　　　　　　　　　　　
  T. Shimada; K. Touji; Y. Katsuyama; Hiroaki Takeda; Tadashi Shiosaki
  JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Volume：27, Number：13-15, First page：3877, Last page：3882, May 2007, [Reviewed]
  Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on BaTiO3-(Bi1/2Na1/2)TiO3 (BT-BNT) solid solution were prepared by a conventional solid state reaction method using high purity reagents. Temperature dependence of the electrical resistivity was measured and a typical PTCR effect was confirmed in the solid solutions up to 30 mol% addition of BNT. Especially 8.8 mol% BNT added sample indicated superior PTCR properties by optimizing the preparation conditions. Thermal electrical properties and crystal structure were investigated in order to elucidate the origin of the PTCR effect in this system. The DSC spectra of this system indicated the transition to cubic from tetragonal crystal structure and the transition temperature increased with BNT addition up to about 175 degrees C. Also the boundary layer on the grains was observed by Scanning Spreading Resistance Microscope (SSRM) technique. And then the broad signal of electron emission concerning the interface states was observed using Isothermal Capacitance Transient Spectroscopy (ICTS) technique. In our study, it was found that the PTCR ceramics in BT-BNT system has extremely similar properties to the conventional lead contained one. (c) 2007 Elsevier Ltd. All rights reserved.
  ELSEVIER SCI LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jeurceramsoc.2007.02.171
  DOI ID：10.1016/j.jeurceramsoc.2007.02.171, ISSN：0955-2219, ORCID：47804532, Web of Science ID：WOS:000248822800064
• Growth of bismuth tungstate Bi2WO6 mono-domain crystals and chemical etching for measuring their electrical properties　　　　　　　　　　　　　　　
  Takeda Hiroaki; Nishida Masaya; Nishida Takashi; Shiosaki Tadashi
  Transactions of the Materials Research Society of Japan, Volume：32, Number：1, First page：11, Last page：14, Jan. 2007, [Reviewed], [Lead, Corresponding]
  ORCID：49173951
• Growth and electric properties of Al-substituted langasite-type La₃Ta_0.5Ga_5.5O₁₄ crystals at high temperature　　　　　　　　　　　　　　　
  Hiroaki Takeda; Satoshi Tanaka; Hiroyuki Shimizu; Takashi Nishida; Tadashi Shiosaki
  Key Engineering Materials, Volume：320, First page：239, Last page：242, Sep. 2006, [Reviewed], [Lead, Corresponding]
  We report an effective substitution of aluminum for gallium in langasite-type La3Ta0.5Ga5.5O14 (LTG) crystals for use in a pressure sensor at high temperature. Al-substituted LTG (La3Ta0.5Ga5.5-xAlxO14; LTGAx) single crystals up to the solubility limit of x=0.5 have been grown by the conventional Czochralski technique. The electric properties of the LTGAx crystals were investigated and compared with those of LTG. By Al substitution, the piezoelectric constant d(11) and the electromechanical coupling factors (k(12)) became slightly larger. The LTGAx crystals showed a lower temperature dependence of d(11) and a higher electric resistivity rho than those of the LTG crystals.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  DOI：https://doi.org/10.4028/0-87849-411-1.239
  DOI ID：10.4028/0-87849-411-1.239, ISSN：1013-9826, ORCID：47804536, Web of Science ID：WOS:000241412900057
• Growth and piezoelectric properties of R₃Ga₅SiO₁₄ and RCa₄O(BO₃)₃ (R: rare-earth elements) single crystals　　　　　　　　　　　　　　　
  H Takeda; H Nakao; S Izukawa; H Shimizu; T Nishida; S Okamura; T Shiosaki
  JOURNAL OF ALLOYS AND COMPOUNDS, Volume：408, First page：474, Last page：479, Feb. 2006, [Reviewed], [Lead, Corresponding]
  R3Ga5SiO14 (RGS, R: rare-earth elements) and RCa4O(BO3)(3) (RCOB) single crystals were synthesized by the Czochralski technique and their piezoelectric properties were investigated. The piezoelectric moduli, d(11) and d(14), of La3Ga5SiO14 are higher than those of Nd(3)Ga(5)SiG(14). Moreover, in the RGS-type crystal, we found that the piezoelectric modulus, d(11), increased with the lattice parameter a. The ionic size preferences of all cation sites in the RGS-type structure were also clarified. Based on these results, a new RGS-type Ba3TaGa3Si2O14 Crystal was synthesized. We have successfully grown RCOB (R=La, Nd, Gd, Dy, and Y) single crystals with 1 and 2 in. diameter dimensions. The surface acoustic wave (SAW) properties of RCOB filters were investigated. In RCOB, the NdCOB single crystal showed the highest electromechanical coupling factors and lowest temperature coefficient of delay of the RCOB crystals. (c) 2005 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE SA, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jallcom.2004.12.108
  DOI ID：10.1016/j.jallcom.2004.12.108, ISSN：0925-8388, ORCID：47804537, Web of Science ID：WOS:000235445300111
• Growth and SAW properties of rare-earth calcium oxoborate crystals　　　　　　　　　　　　　　　
  H Nakao; M Nishida; T Shikida; H Shimizu; H Takeda; T Shiosaki
  JOURNAL OF ALLOYS AND COMPOUNDS, Volume：408, First page：582, Last page：585, Feb. 2006, [Reviewed]
  Rare-earth calcium oxoborate RCa4O(BO3)(3) (R, rare-earth elements; RCOB) (R = Pr, Nd, Sm, Eu, Dy, Ho, Er) bulk single crystals were grown by the Czochralski technique. Their melting temperature increased with a decrement of a rare-earth ion radius in RCOB. Surface acoustic wave (SAW) and pseudo-SAW (PSAW) properties of the RCOB crystal were investigated. The electro mechanical coupling factors k(2) values of NdCOB were the highest of all RCOB crystals. For SAW, k(2) of 0.80% and velocity of 3400m/s at X-axis propagation were obtained on the Y-cut substrate. For PSAW, 1.95% and 3900 m/s at Y-axis propagation were obtained on the Z-cut substrate. Moreover, the thermal stability of the SAW of NdCOB (TCD = 3 ppm/degrees C) is equivalent to a quartz crystal (TCD = 0 ppm/degrees C). (c) 2005 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE SA, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jallcom.2004.12.153
  DOI ID：10.1016/j.jallcom.2004.12.153, ISSN：0925-8388, ORCID：47804538, Web of Science ID：WOS:000235445300133
• X-ray topography on piezoelectric La₃Ga₅SiO₁₄ single crystal
  Yasuhiro Yoneda; Yuka Okajima; Hiroaki Takeda; Tadashi Shiosaki; Jun'ichiro Mizuki
  Transactions of the Materials Research Society of Japan, Volume：31, Number：1, First page：7, Last page：11, Jan. 2006, [Reviewed]
  Piezoelectric La3Ga5SiO14 (LGS) single crystal grown by Czochralski technique was characterized by high-resolution synchrotron X-ray measurements. Crystal quality of the LGS was evaluated by the rocking curve width of 16.75 arcsec. Due to the growth problem (homogeneity and faceting habit), the crystal quality of the LGS was worth than we expected. Diffraction topography revealed inhomogeneity of the LGS crystal. Super lattice structure indicating a Ga/Si ordering of 2d (space group P321) site was observed. Weak broad peaks indicating a glassy behavior were also observed. These extra peaks are the first observation in LGS crystal and they are also the origin of degradation of the crystal quality.
  ELSEVIER SCIENCE BV, English, International conference proceedings
  ORCID：49173953, Web of Science ID：WOS:000240547200002
• Growth and characterization of langasite-type single crystals substituted with aluminum to the solubility limit
  Hiroaki Takeda; Satoshi Tanaka; Tadashi Nishida; Kiyoshi Uchiyama; Tadashi Shiosaki
  Transactions of the Materials Research Society of Japan, Volume：31, Number：1, First page：11, Last page：14, Jan. 2006, [Reviewed], [Lead, Corresponding]
  We describe the process to grow the aluminum-substituted langasite-type, La3Ta0.5Ga5.5-xAlxO14 (LTGAx), single crystals with a uniform Al concentration by the conventional Czochralski technique. The solid-state reaction of the raw material powders was performed for an investigation of the Al substitution limit. The results showed that the LTGAx polycrystals have the wide solid-solution range of 0 <= x <= 2.0. The LTGAx single crystals with 0 <= x <= 1.0 were grown on the basis of the pseudo binary phase diagram, where one of the end members is the pure La3Ta0.5Ga5.5O14 (LTG) phase. The Al content x in these LTGAx single crystals decreases with the growth process. In this study, we obtained LTGAx single crystals up to x=0.5 without any inclusions, but with a small change in the chemical composition. The piezoelectric moduli d(11) and d(14) values of the LTGA0.5 crystals are greater than those of the pure LTG ones.
  ELSEVIER SCIENCE BV, English, International conference proceedings
  ORCID：49173952, Web of Science ID：WOS:000240547200003
• Estimation of parasitic capacitance in measurement of hysteresis properties of ferroelectric microcapacitors using scanning probe microscope　　　　　　　　　　　　　　　
  S Okamura; T Iwase; H Takeda; T Nishida; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：44, Number：11, First page：8062, Last page：8065, Nov. 2005, [Reviewed]
  Parasitic capacitances in the measurement of the hysteresis properties of ferroelectric microcapacitors are estimated. A scanning probe microscope with a conductive cantilever was used for contacting various-sized Pb(Zr,Ti)O(3) (PZT) microcapacitors fabricated by electron-beam-induced patterning. A parasitic capacitance under the condition in which the cantilever was lifted up by 40 mu m from the contact point was estimated to be 0.88 pF. Although all the PZT microcapacitors showed well-saturated hysteresis curves with compensation for the parasitic capacitance of 0.88pF, the slopes of the compensated hysteresis curves around the maximum field increased with decreasing capacitor area. From the capacitor area dependence of the slopes, the increase in parasitic capacitance caused by bringing the cantilever near substrates for contact was estimated to be 0.049 pF. This increased parasitic capacitance evidently decreased the apparent coercive fields of the PZT microcapacitors with areas lower than 10 mu m(2) while it had no influence on remanent polarization.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.44.8062
  DOI ID：10.1143/JJAP.44.8062, ISSN：0021-4922, ORCID：47804544, Web of Science ID：WOS:000233437400067
• Dielectric, elastic and piezoelectric constants of lanthanum calcium oxoborate single crystals with monoclinic structure of point group m　　　　　　　　　　　　　　　
  H Shimizu; T Nishida; M Nishida; H Takeda; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：44, Number：9B, First page：7059, Last page：7063, Sep. 2005, [Reviewed]
  In this study, we propose using the d33 mode of a 03101 meter, new cuts and vibration modes to evaluate electroacoustical constants (dielectric, elastic and piezoelectric constants) of a piezoelectric crystal belonging to point group m. All material constants at room temperature of lanthanum calcium oxoborate LaCa4O(BO3)(3) single crystals were thereby determined. The piezoelectric constants d(11) and d(33) measured by the d33 meter were 2.1 and 1.5 pC/N, respectively. The others were determined by the resonance-antiresonance method using various cuts in which the length-extensional mode and/or face-shear mode can be generated. The elastic compliances S-44(E), S-55(E) and S-66(E) were 35 x 10(-12), 18 x 10(-12) and 18 x 10(-12) m(2)/N, respectively. Moreover, in order to investigate the dependence of the Rayleigh surface acoustic wave (RSAW) velocity and coupling coefficient k(2) on propagation direction, theoretical analysis by computer simulations was carried out for the Z-cut using the elastic compliances obtained in this study. The dependence of RSAW velocity on propagation direction calculated using the elastic compliances obtained did not agree with measurement results, but the calculated results were significantly improved and closer to measurement results.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.44.7059
  DOI ID：10.1143/JJAP.44.7059, ISSN：0021-4922, ORCID：47804541, Web of Science ID：WOS:000232570700044
• BaTiO₃-(Bi_1/2Na_1/2)TiO₃ solid-solution semiconducting ceramics with T_c > 130^oC　　　　　　　　　　　　　　　
  H Takeda; W Aoto; T Shiosaki
  APPLIED PHYSICS LETTERS, Volume：87, Number：10, First page：102104, Sep. 2005, [Reviewed], [Lead, Corresponding]
  As a candidate of a lead-free positive temperature coefficient of resistivity (PTCR) material, barium titanate (BaTiO3)-based solid-solution ceramics, Ba1-x(Bi1/2Na1/2)(x)TiO3 with x=0.05 (BBNT5), have been synthesized by an ordinary sintering technique. Temperature dependences of the dielectric and ferroelectric properties show ferroelectric and paraelectric phase transition of the ceramics with the Curie temperature of T-c = 170 degrees C, which is higher than that of BaTiO3 (130 degrees C). The La-doped BBNT5 ceramics display low rho values of 10(2)-10(3) Omega cm at room temperature and their abrupt changes of 10(2)-10(4) at about 220 degrees C. The reduced BBNT5 ceramics show small PTCR characteristics compared to the La-doped ones. (c) 2005 American Institute of Physics.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.2042551
  DOI ID：10.1063/1.2042551, ISSN：0003-6951, ORCID：47804539, Web of Science ID：WOS:000231614800030
• Enhanced piezoelectric properties of off-stoichiometric strontium bismuth tantalate Sr_0.8Bi_2.2Ta₂O₉ ceramics　　　　　　　　　　　　　　　
  H Takeda; C Fujioka; R Aoyagi; S Okamura; T Shiosaki
  APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, Volume：81, Number：1, First page：131, Last page：135, Jun. 2005, [Reviewed], [Lead, Corresponding]
  The piezoelectric properties of strontium bismuth tantalate SrBi2Ta2O9 (SBT) ceramics were enhanced by introducing off-stoichiometry into the starting materials. Sr-deficient and Bi-excess SBT, Sr0.8Bi2.2Ta2O9 (S0.8B2.2T), ceramic samples were prepared by a conventional ceramic technique. The optimum poling conditions (temperature T-p, time t(p), and electric field E-p) were investigated for the piezoelectric measurement. All the obtained independent electromechanical coupling factors of the S0.8B2.2T dense ceramics were as follows: k(p)=10.6, k(31)=6.8, k(33)=14.0, k(15)=7.8, and k(t)=16.2%. The physical constants of the S0.8B2.2T ceramics were also determined. The piezoelectric constants were d(33)=13.0, d(31)=6.0, and d(15)=10.2 pC/N.
  SPRINGER, English, Scientific journal
  DOI：https://doi.org/10.1007/s00339-004-3073-4
  DOI ID：10.1007/s00339-004-3073-4, ISSN：0947-8396, ORCID：47804543, Web of Science ID：WOS:000228794000022
• Crystal growth of bismuth tungstate Bi₂WO₆ by slow cooling method using borate fluxes　　　　　　　　　　　　　　　
  H Takeda; T Nishida; S Okamura; T Shiosaki
  JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Volume：25, Number：12, First page：2731, Last page：2734, Apr. 2005, [Reviewed], [Lead, Corresponding]
  Ferroelectric Bi2WO6 (BWO) single crystals have been grown by a flux method below the phase transition (ferro- to paraelectric) temperature. Sodium chloride, LiBO2, Li2B4O7 (LBO), Na2B4O7 (NBO) and NaB(4)O(7)center dot 10H(2)O were selected as the flux. We found that LBO and NBO are suitable flux materials for crystal growth. The phase diagram of the BWO-LBO(NBO) system was investigated by the combination of the differential thermal analysis and the quench method. In the BWO-LBO(NBO) binary system, the mixtures of the end members without intermediate compounds were observed. On the basis of the phase diagram, we have obtained plate-like crystals with sizes up to 0.7 mm thickness from the solidified melts with the mole ratio BWO:LBO of 7:3. The crystals are single domain, yellow in color, and have well developed smooth {0 0 1} faces. The dielectric constant, epsilon(33)/epsilon(0), of the crystals is 90 at room temperature and the ferroelectric behavior is available. (c) 2005 Elsevier Ltd. All rights reserved.
  ELSEVIER SCI LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jeurceramsoc.2005.03.184
  DOI ID：10.1016/j.jeurceramsoc.2005.03.184, ISSN：0955-2219, ORCID：47804540, Web of Science ID：WOS:000230569300156
• Effect of non-stoichiometry on ferroelectricity and piezoelectricity in strontium bismuth tantalate ceramics　　　　　　　　　　　　　　　
  C Fujioka; R Aoyagi; H Takeda; S Okamura; T Shiosaki
  JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Volume：25, Number：12, First page：2723, Last page：2726, Mar. 2005, [Reviewed], [Corresponding]
  The effect of non-stoichiometry on the ferroelectricity and piezoelectricity of strontium bismuth tantalate, SrBi2Ta2O9, has been studied using ordinarily fired ceramics. Sr1-xBi2+xTa2O9 (x = 0.0-0.3) [SBT(x)] ceramics were prepared by a conventional ceramic technique and sintered at 1200 degrees C. The remanent polarization, P-r, and the electric coercive field, E-c, increase with a change in the composition x. The electromechanical coupling factors (k(p) and k(33)) and mechanical quality factors Q(m) increase up to around x = 0.2, but decreases at x > 0.2 as the composition x increases. The reduction of the piezoelectric properties at x > 0.2 is associated with the decrease in the electric resistivity of the SBT(x) ceramics. Both the ferroelectric and piezoelectric properties of the SBT(x) ceramics are basically enhanced by the Bi substitution. (c) 2005 Elsevier Ltd. All rights reserved.
  ELSEVIER SCI LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/j.jeurceramsoc.2005.03.129
  DOI ID：10.1016/j.jeurceramsoc.2005.03.129, ISSN：0955-2219, ORCID：47804542, Web of Science ID：WOS:000230569300154
• Growth, Structure and Piezoelectric Properties of Ln3Ga5SiO14 (Ln= La, Nd) Single Crystals　　　　　　　　　　　　　　　
  Takeda Hiroaki; Izukawa Shintaro; Shimizu Hiroyuki; Nishida Takashi; Okamura Soishiro; Shiosaki Tadashi
  Transactions of the Materials Research Society of Japan, Volume：30, First page：63, Last page：66, Jan. 2005, [Reviewed], [Lead, Corresponding]
  ORCID：49173954
• Ferroelectric and piezoelectric properties of bismuth layered-structure ferroelectric (Sr,Na,Bi)Bi₂Ta₂O₉ ceramics　　　　　　　　　　　　　　　
  R Aoyagi; H Takeda; S Okamura; T Shiosaki
  MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, Volume：116, Number：2, First page：156, Last page：160, Jan. 2005, [Reviewed], [Corresponding]
  Sodium strontium bismuth tantalate (1 - x)[Na0.5Bi2.5Ta2O9]-x[Sr0.8Bi2.15Ta2O9] (NSBT-x) solid solution ceramics were synthesized by an ordinary firing method. The ferroelectric and piezoelectric properties of the NSBT-x ceramics were characterized. A single phase with the ABi(2)Ta(2)O(9)-type structure was obtained over the entire composition range. The Curie temperature, T-c, linearly decreased with an increase in x from 780degreesC (x = 0) to 410degreesC (x = 1.0). Well-developed P(polarization)-E(electric field) hysteresis loops were observed for all samples. The observed P-r-values were independent of the composition x. The coercive field, E-c, changed with the composition x and the maximum value of 72 kV/cm was obtained in the NSBT-0.25 ceramics. Superior piezoelectric properties were observed for the NSBT-0.75 ceramics sintered at 1200 degreesC. The maximum electromechanical coupling factors and mechanical quality factor were k(p) = 9.0%, k(33) = 15.4% and Q,,(kp) = 7000, respectively. (C) 2004 Elsevier B.V. All rights reserved.
  ELSEVIER SCIENCE SA, English, Scientific journal
  DOI：https://doi.org/10.1016/j.mseb.2004.09.025
  DOI ID：10.1016/j.mseb.2004.09.025, ISSN：0921-5107, ORCID：47804545, Web of Science ID：WOS:000226257200009
• Piezoelectric properties of sodium bismuth tantalate Na_0.5Bi_2.5Ta₂O₉ dense ceramics　　　　　　　　　　　　　　　
  M Matsushita; R Aoyagi; H Takeda; S Okamura; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, Volume：43, Number：10, First page：7164, Last page：7168, Oct. 2004, [Reviewed], [Corresponding]
  The piezoelectric properties of sodium bismuth tantalale Na0.5Bi2.5Ta2O9 (NBTa) dense ceramic, were determined using 0.1 wt% Mn-doped samples. The ferroelectric properties of the NBTa ceramics were confirmed. The remanent polarization P-r and coercive field E-c were 15.5 muC/cm(2) and 81.5 kV/cm at room temperature, respectively. Optimum poling conditions (temperature T-p, time t(p) and electric field E-p) were investigated for piezoelectric measurements. The independent electromechanical coupling factors of the NBTa dense ceramics were obtained as follows: k(p) = 10.0, k(31) = 6.1, k(33) = 12.4 and k(15) = 5.6%. These values are comparable to those of the reported bismuth layer-structured ferroelectrics (BLSFs) that are composed of two pseudo-perovskite layers. The physical constants of the NBTa ceramics were also determined. The piezoelectric constants were d(33) = 10.8, d(31) = 5.2, and d(15) = 6.0 pC/N.
  INST PURE APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.43.7164
  DOI ID：10.1143/JJAP.43.7164, ISSN：0021-4922, ORCID：47804550, Web of Science ID：WOS:000224780300068
• Evaluation of material constants and temperature properties in lanthanum calcium oxoborate LaCa₄O(BO₃)₃ single crystals　　　　　　　　　　　　　　　
  H Shimizu; K Kodama; H Takeda; T Nishida; T Shikida; S Okamura; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：43, Number：9B, First page：6716, Last page：6720, Sep. 2004, [Reviewed]
  Lanthanum calcium oxoborate LaCa(4)O(BO(3))(3) (LaCOB) single crystals were successfully grown by the Czochralski technique. It was found that LaCOB crystals belong to the monoclinic system (point group m) and the total number of independent material constants that should be determined is 27. Twenty-four of the 27 material constants at room temperature were determined by the resonance-antiresonance method. The normalized first-order temperature coefficients of some constants e.g., epsilon(11)(,)(T) epsilon(22)(T), epsilon(33)(T) and epsilon(13)(T) determined at 10 kHz were 56.30, -273.6, 135.8 and -258.4 and d(11) l and d(12) were -408.3 and 83.60ppm/degreesC, respectively. Additionally, the thermal expansion coefficients e.g., alpha(11), alpha(22) and alpha(33) determined on a single crystal cut along the X, Y and Z rectangular directions by the thermodilatometry measurement were 7.36 x 10(-6), 8.17 x 10(-6) and 11.4 x 10(-6)/degreesC, respectively. As a result of the evaluation, most of the material constants and temperature properties necessary for investigating the properties of piezoelectric devices typified by SAW were obtained.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.43.6716
  DOI ID：10.1143/JJAP.43.6716, ISSN：0021-4922, ORCID：47804547, Web of Science ID：WOS:000224736400044
• Growth and characterization of piezoelectric Ba₃TaGa₃Si₂O₁₄ single crystals
  H Takeda; S Izukawa; S Okamura; T Shiosaki
  Key Engineering Materials, Volume：269, First page：23, Last page：26, Aug. 2004, [Reviewed], [Lead, Corresponding]
  Piezoelectric Ba3TaGa3Si2O14 (abbreviated BTGS) single crystals were grown by the Czochralski technique using raw materials with a stoichiometric composition. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data. The results showed that each metal occupies its respective crystallographic site in an ordered way. The surface acoustic wave properties of BTGS were also investigated. The maximum k(2) values in the Y-cut BTGS wafer was about 0.43% for the X-axis propagation. This value is larger than those of the isomorphic compound La3Ga5SiO14 of which filters have been mass-produced for a use in a wideband-code division multiple access station.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  ISSN：1013-9826, ORCID：47804549, Web of Science ID：WOS:000224025500006
• Piezoelectric Properties of Strontium Bismuth Tantalate Sr_xBi_3-xTa₂O₉ Dense Ceramics
  Takeda Hiroaki; Fujioka Chie; Aoyagi Rintaro; Okamura Soichiro; Shiosaki Tadashi
  Journal of the Ceramic Society of Japan, Supplement, Volume：112, First page：S510, Last page：S513, May 2004, [Reviewed], [Lead, Corresponding]
  DOI：https://doi.org/10.14852/jcersjsuppl.112.0.S510.0
  DOI ID：10.14852/jcersjsuppl.112.0.S510.0, ORCID：47804551
• Ferroelectric and piezoelectric properties of strontium bismuth tantalate ceramics　　　　　　　　　　　　　　　
  H Takeda; C Fujioka; R Aoyagi; S Okamura; T Shiosaki
  Key Engineering Materials, Volume：264-268, First page：1169, Last page：1172, May 2004, [Reviewed], [Lead, Corresponding]
  The ferroelectric and piezoelectric properties of strontium bismuth tantalate SrxBiyTa2O9 (SrxBiyT) ceramics were investigated. Well developed P(polarization)- E(electric field) hysteresis loops were observed for all samples except for the Sr1.0BiyT(y>2) ceramics. A large remanent polarization (2P(r) = 26 muC/cm(2)) was observed for the Sr0.8Bi2.15T ceramics sintered at 1150degreesC. For the Sr0.8Bi2.2T ceramics, the determined electromechanical coupling factor (k(p) = 9.7%) and mechanical quality factor (Q(m) = 4500) with a radial-extensional mode were obtained. Those of the stoichiometric SBT ceramics are k(p) = 4.0%. The cation vacancy and/or Bi incorporation into the Sr site of SrBi2Ta2O9 were effective for enhancement of the electromechanical coefficients.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.264-268.1169
  DOI ID：10.4028/www.scientific.net/KEM.264-268.1169, ISSN：1013-9826, ORCID：47804548, Web of Science ID：WOS:000223059700276
• Electrical properties of Na_0.5Bi_2.5Ta₂O₉-Sr_1-xBi_2+yTa₂O₉ solid solution ceramics　　　　　　　　　　　　　　　
  H Takeda; R Aoyagi; S Okamura; T Shiosaki
  Key Engineering Materials, Volume：264-268, First page：1241, Last page：1244, May 2004, [Reviewed], [Lead, Corresponding]
  The (1-x)[Na0.5Bi2.5Ta2O9] - x[Sr0.8Bi2.15Ta2O9] (0less than or equal toxless than or equal to1) solid solution ceramics were synthesized using a conventional sintering method. All the ceramic samples consisted of a single phase with an orthorhombic symmetry A2(1)am and showed well-developed polarization-electric field hysteresis loops. The temperature dependence of the dielectric constant revealed that the Curie temperature T-c linearly decreased with ail increase in x from 780degreesC(x=0) to 410degreesC(x=1.0). The maximum electromechanical coupling factor (k(p)=8.6%) and mechanical quality factor (Q(m)=7000) with a radial-extensional mode were obtained for the x=0.75 samples.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.264-268.1241
  DOI ID：10.4028/www.scientific.net/KEM.264-268.1241, ISSN：1013-9826, ORCID：47804546, Web of Science ID：WOS:000223059700294
• Growth and characterization of lanthanum calcium oxoborate LaCa₄O(BO₃)₃ single crystals　　　　　　　　　　　　　　　
  H Takeda; H Sako; H Shimizu; K Kodama; M Nishida; H Nakao; T Nishida; S Okamura; T Shikida; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, Volume：42, Number：9B, First page：6081, Last page：6085, Sep. 2003, [Reviewed], [Lead, Corresponding]
  Lanthanum calcium oxoborate LaCa4O(BO3)(3) (LaCOB) bulk single crystals were grown by the Czochralski technique. The crystals have almost constant transmittances between 320 and 2500 nm. The relationship between the growth habit and crystallographic abc - rectangular XYZ axes was clarified. Some dielectric and piezoelectric constants as well as elastic compliance constants of the LaCOB crystals were evaluated. The surface acoustic wave (SAW) and pseudo-SAW (PSAW) parameters of the LaCOB crystals were also measured. For the SAW, the largest electromechanical coupling coefficient of approximately 0.26% and a velocity of 3550 m/s were obtained for the YX orientation. For the PSAW, these parameters were approximately 0.6% and 4000 m/s for the ZY orientation.
  JAPAN SOC APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/jjap.42.6081
  DOI：https://doi.org/10.1143/JJAP.42.6081
  DOI ID：10.1143/jjap.42.6081, ISSN：0021-4922, ORCID：47804554, Web of Science ID：WOS:000186948300042
• Cation distribution and melting behavior of La₃Ga₅M⁴⁺O₁₄ (M = Si, Ti, Ge, Zr, Sn, and Hf) crystals　　　　　　　　　　　　　　　
  H Takeda; R Aoyagi; S Okamura; T Shiosaki
  FERROELECTRICS, Volume：295, First page：661, Last page：670, Jun. 2003, [Reviewed], [Lead, Corresponding]
  The crystal structure of La3Ga5M4+O14 (M=Si, Ti, Ge, Zr, Sn, and Hf) was refined from its powder x-ray diffraction data. These compounds were confirmed to be isostructural to Ca3Ga2Ge4O14 (P321(No.150), Z=1) and the site preference of M atoms was determined. Si and Ge atoms occupy only the smaller tetrahedral (2d) sites, Ti atoms occupy both octahedral (1a) and tetrahedral (3f) sites, and the others (Zr, Sn, and Hf) all occupy the octahedral (1a) sites. Single crystals were grown by a slow cooling method using raw materials with stoichiometric compositions. An analysis of growing process showed that the La3Ga5M4+O14 (M=Si and Ge) crystal congruently melts, and that the other compounds incongruently melt and are peritectic compounds.
  TAYLOR & FRANCIS LTD, English, Scientific journal
  DOI：https://doi.org/10.1080/00150190390239396
  DOI ID：10.1080/00150190390239396, ISSN：0015-0193, ORCID：47804552, Web of Science ID：WOS:000186527400009
• Influence of a TiO₂ adhesion layer on the structure and the orientation of a Pt layer in Pt/TiO₂/SiO₂/Si structures　　　　　　　　　　　　　　　
  N Abe; Y Otani; M Miyake; M Kurita; H Takeda; S Okamura; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, Volume：42, Number：5A, First page：2791, Last page：2795, May 2003, [Reviewed]
  Three kinds of TiO2 layers were formed on SiO2/Si substrates: (200)-oriented TiO2 with rutile structure, (103)-oriented TiO2 with anatase structure and randomly oriented TiO2. All the Pt films deposited on the TiO2 layers had (I 11) orientation. Pt films deposited on the rutile TiO2 had a columnar structure and the full-width at half maximum (FWHM) of the rocking curve of the Pt(I 11) plane was estimated to be 0.88degrees. The diffusion of TiO2 to the surface of the Pt films hardly occurred in the case of rutile TiO2. The FWHM of the rocking curve of Pt(l 11) formed on anatase TiO2 was estimated to be 1.55degrees. The rocking curve of Pt(l 11) formed on randomly oriented TiO2 consisted of two peaks with centers separated by 6.25degrees. The diffusion of TiO2 to the surface was observed in the cases of anatase and randomly oriented TiO2. From these results, we concluded rutile TiO2 fabricated by metal deposition and subsequent oxidation was the best material for high-quality bottom Pt electrodes.
  INST PURE APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.42.2791
  DOI ID：10.1143/JJAP.42.2791, ISSN：0021-4922, ORCID：47804555, Web of Science ID：WOS:000183744900051
• Crystal structure and electromechanical coupling properties of Na_0.5Bi_2.5Ta₂O₉ dense ceramics　　　　　　　　　　　　　　　
  H Takeda; R Aoyagi; M Matsushita; T Shiosaki
  APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, Volume：76, Number：2, First page：295, Last page：297, Feb. 2003, [Reviewed], [Lead, Corresponding]
  The crystal structure of sodium bismuth tantalate, Na0.5Bi2.5Ta2O9, was analyzed by the powder X-ray-diffraction Rietveld method. The distribution of Na atoms was found to be ordered in the A site of the pseudo-perovskite (ATa(2)O(7))(2-) blocks. The piezoelectric properties were effectively examined using dense bulk ceramics containing manganese oxide as the dopant. The electromechanical coupling coefficients (k(ij)) and the electrical quality factors (Q(m)) are k(p) = 10%, k(31) = 8.3%, k(t) = 19.7%, and Q(m) = 3000.
  SPRINGER-VERLAG, English, Scientific journal
  DOI：https://doi.org/10.1007/s00339-002-1714-z
  DOI ID：10.1007/s00339-002-1714-z, ISSN：0947-8396, ORCID：47804553, Web of Science ID：WOS:000179782000030
• Synthesis and electrical properties of sodium bismuth niobate Na_0.5Bi_2.5Nb₂O₉　　　　　　　　　　　　　　　
  R Aoyagi; H Takeda; S Okamura; T Shiosaki
  MATERIALS RESEARCH BULLETIN, Volume：38, Number：1, First page：25, Last page：32, Jan. 2003, [Reviewed]
  The crystal structure of Na0.5Bi2.5Nb2O9 was refined from its powder X-ray diffraction (XRD) data. Sodium bismuth niobate at 23 degreesC is orthorhombic, A2(1)am, with a = 5.4998(3) Angstrom, b = 5.4602(2) Angstrom, c = 24.952(l) Angstrom, and Z = 4. The piezoelectric properties were investigated using the dense bulk ceramics. The electromechanical coupling coefficients (k(ij)) and electrical quality factors (Q(m)) are k(31) = 3.2%, k(1) = 10.0%, and Q(m) = 3800. Single crystals were also grown from stoichiometric melts using a slow cooling technique. The dielectric and ferroelectric properties of the crystal indicates that a spontaneous polarization clearly occurs in the crystallographic a-b plane. (C) 2002 Elsevier Science Ltd. All rights reserved.
  PERGAMON-ELSEVIER SCIENCE LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/S0025-5408(02)01001-2
  DOI ID：10.1016/S0025-5408(02)01001-2, ISSN：0025-5408, eISSN：1873-4227, ORCID：47804556, Web of Science ID：WOS:000180718200004
• Synthesis and characterization of Ba₃MeGa₃Si₂O₁₄ (Me=Nb⁵⁺, Ta⁵⁺) crystal　　　　　　　　　　　　　　　
  Takeda Hiroaki; Nishida Takashi; Okamura Soichiro; Shiosaki Tadashi
  Transactions of the Materials Research Society of Japan, Volume：28, Number：1, First page：181, Last page：184, Jan. 2003, [Reviewed], [Lead, Corresponding]
  ORCID：49173955
• Evaluation of electrical polarizability and in vitro bioactivity of apatite Sr₅(PO₄)₃OH dense ceramics　　　　　　　　　　　　　　　
  H Takeda; Y Seki; S Nakamura; K Yamashita
  JOURNAL OF MATERIALS CHEMISTRY, Volume：12, Number：8, First page：2490, Last page：2495, Aug. 2002, [Reviewed], [Lead, Corresponding]
  Dense ceramics of Sr-5(PO4)(3)OH (strontium hydroxide tris-phosphate with all apatite structure; Sr-HAp) with little dehydration were successfully synthesized in a humid atmosphere. Polarization of these Sr-HAp ceramics was performed by application of an external dc field at higher temperature. To clarify the polarization and depolarization phenomena of Sr-HAp, the polarized samples were analyzed by thermally stimulated depolarization current (TSDC) measurement. The features of the TSDC spectra were very similar to those of the isomorphic hydroxyapatite (Ca-5(PO4)(3)OH; HAp); moreover, the charges of sub-millicoulomb order Could be stored in the polarized Sr-HAp. The results of in vitro characterization of polarized Sr-HAp ceramics were comparable to those observed on HAp with high biocompatibility, showing the acceleration of bone-like crystal growth on negatively charged ceramic surfaces by electrical polarization. These findings provide evidence that the surface charge of these apatite materials with hydroxide ions promotes the biological reaction.
  ROYAL SOC CHEMISTRY, English, Scientific journal
  DOI：https://doi.org/10.1039/b202262c
  DOI ID：10.1039/b202262c, ISSN：0959-9428, ORCID：47804558, Web of Science ID：WOS:000177525600064
• Chemical etching of lanthanum gallium silicate La₃Ga₅SiO₁₄ single crystals　　　　　　　　　　　　　　　
  H Takeda; S Okamura; T Shiosaki
  JOURNAL OF MATERIALS SCIENCE LETTERS, Volume：21, Number：14, First page：1117, Last page：1119, Jul. 2002, [Reviewed], [Lead, Corresponding]
  KLUWER ACADEMIC PUBL, English, Scientific journal
  DOI：https://doi.org/10.1023/A:1016566718494
  DOI ID：10.1023/A:1016566718494, ISSN：0261-8028, ORCID：47804557, Web of Science ID：WOS:000177007600014
• Synthesis and ferroelectric properties of M_0.5Bi_2.5Ta₂O₉ (M = Na, K) ceramics　　　　　　　　　　　　　　　
  K Komagata; H Takeda; T Shiosaki
  JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, Volume：110, Number：4, First page：255, Last page：258, Apr. 2002, [Reviewed], [Corresponding]
  Bismuth layer-structured ferroelectrics (BLSFs), M0.5Bi2.5Ta2O9 (M =Na, K) were synthesized using a solidstate reaction. Na0.5Bi2.5Ta2O9 (NBT) single phase polycrystals were obtained by heating raw material powders at 1100degreesC. On the other hand, K0.5Bi2.5Ta2O9 (KBT) powder contained KTaO3 as a main impurity phase. Dense ceramics of NBT were prepared by considering Bi2O3 vaporization and using a binder. Result of dielectric and ferroelectric characterizations of the NBT ceramic were as follows: Curie temperature, T-C= 780degreesC, dielectric constant, epsilon(s)=158, dielectric loss factor, tan delta=0.011 as measured at room temperature and 1 MHz and the remanent polarization, P-r = 15-18 muC . cm(-2). The Pr value is the largest among reported BLSFs that are composed of two perovskite layers.
  CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI, English, Scientific journal
  DOI：https://doi.org/10.2109/jcersj.110.255
  DOI ID：10.2109/jcersj.110.255, ISSN：1882-0743, eISSN：1348-6535, ORCID：47804561, Web of Science ID：WOS:000178328100009
• Structure and piezoelectric properties of Al-substituted langasite (La₃Ga_5-xAl_xSiO₁₄) crystals
  H Takeda; M Kumatoriya; T Shiosaki
  Key Engineering Materials, Volume：216, First page：43, Last page：46, Jan. 2002, [Reviewed], [Lead, Corresponding]
  Al-substituted langasite crystals, La3Ga5-xAlxSiO14, were grown by the conventional Czochraiski technique. Using these crystals, their structure and piezoelectric properties were investigated. Xray structural analysis indicated that Al occupied the octahedral site and the two kinds of tetrahedral sites in the crystal lattice. The electromechanical coupling factors (k(12), k(25) and k(26)) of the Al-substituted langasite crystals were found to be larger than those of the Al-free one. Al-substituted langasite is expected to be suitable for use in both bulk- and surface-acoustic wave devices in the next generation of mobile communications.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  ISSN：1013-9826, ORCID：47804566, Web of Science ID：WOS:000172619400011
• Synthesis and electric properties of (Na,Bi)Bi₂Ta₂O₉ ceramics with bismuth layer-structure
  K Komagata; H Takeda; S Okamura; T Shiosaki
  Key Engineering Materials, Volume：228-229, First page：215, Last page：218, Jan. 2002, [Reviewed], [Corresponding]
  The synthesis of ferroelectric Na0.5-xBi2.5+x/3Ta2O9 (NBT) was performed using a conventional solid state reaction. X-ray diffractometry showed that an NBT single phase polycrystalline was obtained for x= 0 and 0.1. Dense NBT ceramics were prepared via ordinary firing (OF), and used for the characterization of the ferroelectric, dielectric and piezoelectric properties. The largest remanent polarization, 2P(r)=36 muC.cm(-2), was obtained at the stoichiometric composition of x=0. The electromechanical coupling factors for the OF specimens were more than twice those of the other bismuth layer-structure ferroelectric ceramics.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  ISSN：1013-9826, ORCID：47804560, Web of Science ID：WOS:000177771700037
• Influence of Bi-contents on electric properties of strontium bismuth tantalate ceramics
  K Komagata; S Okamura; H Takeda; T Shiosaki
  Key Engineering Materials, Volume：228-229, First page：219, Last page：222, Jan. 2002, [Reviewed]
  The synthesis of the bismuth layer-structured ferroelectric, SrxBiyTa2O9 (SBT; x=0.7-1.0, y=2.00-2.30), ceramics was attempted using a conventional solid-state reaction. Sintering was carried out at 1150degreesC for 2 h to prevent vaporization of the bismuth oxide. SBT ceramics with a random orientation were obtained. The ferroelectric properties along the directions parallel and perpendicular to the pressing direction were measured for these SBT ceramics. The maximum values of the remanent polarization (2P(r)) for x=0.7, 0.8, 0.9, and 1.0 were obtained at Bi contents of y=2.23, 2.15, 2.10, and 2.00 in both directions, respectively.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  ISSN：1013-9826, ORCID：47804559, Web of Science ID：WOS:000177771700038
• Effect of aluminum substitution in La₃Ga₅SiO₁₄ crystals on their structure and piezoelectricity　　　　　　　　　　　　　　　
  H Takeda; M Kumatoriya; T Shiosaki
  APPLIED PHYSICS LETTERS, Volume：79, Number：25, First page：4201, Last page：4203, Dec. 2001, [Reviewed], [Lead, Corresponding]
  We report La3Ga5-xAlxSiO14 (0 less than or equal tox less than or equal to1) crystals, with a Ca3Ga2Ge4O14-type structure, suitable for piezoelectric application. A single-crystal x-ray structure analysis reveals that Al atoms are distributed in all cation sites except for the decahedral one occupied by La, by rather favoring the smallest tetrahedral one. The piezoelectric modulus \d(11)\ increased similar to1.3% and d(14) decreased similar to7.7% with the increasing Al content, x, up to 1.0. We discuss the possible correlation between the atomic displacement and the observed compositional dependence of the piezoelectric modulus parallel tod(11)parallel to by referring to other isomorphs. The optimal solid-solution compositions and the use of Al substitution for obtaining the maximum electromechanical coupling factors (k(12), k(25), and k(26)) are advanced. (C) 2001 American Institute of Physics.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.1426274
  DOI ID：10.1063/1.1426274, ISSN：0003-6951, ORCID：47804563, Web of Science ID：WOS:000172682300044
• Crystal growth and characterization of lanthanum substituted bismuth titanate single crystals　　　　　　　　　　　　　　　
  R Aoyagi; H Takeda; S Okamura; T Shiosaki
  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS, Volume：40, Number：9B, First page：5671, Last page：5674, Sep. 2001, [Reviewed]
  The thermostability of lanthanum substituted bismuth titanate, Bi4-xLaxTi3O12 (BLT), with La-content up to x = 0.75 was investigated using differential thermal analysis. Subsequently, BLT and Bi4Ti3O12 (BIT) single crystals were grown by a self-flux method. The BLT crystals with two different ranges of La content, x = 1.0-1.5 and 0 < x < 0.1, were obtained using starting materials with mole ratio BLT(x = 0.25) : Bi2O3 = 1 : 9. Segregation phenomena of La during crystal growth process were observed. A comparison of dielectric and ferroelectric properties in BIT and BLT crystals was performed. The La incorporation led to a significant increase in the coercive field value, E-c, of BIT single crystals.
  INST PURE APPLIED PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1143/JJAP.40.5671
  DOI ID：10.1143/JJAP.40.5671, ISSN：0021-4922, ORCID：47804562, Web of Science ID：WOS:000172075600041
• Proton transport polarization and depolarization of hydroxyapatite ceramics　　　　　　　　　　　　　　　
  S Nakamura; H Takeda; K Yamashita
  JOURNAL OF APPLIED PHYSICS, Volume：89, Number：10, First page：5386, Last page：5392, May 2001, [Reviewed]
  Polarization of sintered hydroxyapatite (HAp) ceramics by application of an external dc field at higher temperature was analyzed by thermally stimulated depolarization current (TSDC) measurements. The mechanisms for the polarization and depolarization of HAp were discussed in relation to the instability of the protons in the hydroxide groups. The TSDC spectra consisted of broad peaks, while the ferroelectric substances such as the BaTiO3 ceramics exhibited a sharp peak. Although the maximum current density of 7.87 nA cm(-2) for the HAp polarized at 400 degreesC under 1.0 kV cm(-1) was approximately 1/12 lower than that of BaTiO3, the polarization charge of 14.9 muC cm(-2) was almost twice as large as that of BaTiO3. Considering the activation energy of 0.72-0.89 eV for the depolarization, it was revealed that the polarization of HAp was ascribed to the migration of protons in the columnar OH- channels with a micrometer-order distance. It was also found that the polarization charge was large and long enough to enhance the biological reactivity of HAp ceramics for biomedical implants. (C) 2001 American Institute of Physics.
  AMER INST PHYSICS, English, Scientific journal
  DOI：https://doi.org/10.1063/1.1357783
  DOI ID：10.1063/1.1357783, ISSN：0021-8979, ORCID：47804565, Web of Science ID：WOS:000168438400021
• Effect of starting melt composition on growth of La₃Ta_0.5Ga_5.5O₁₄ crystal　　　　　　　　　　　　　　　
  H Takeda; T Fukuda; H Kawanaka; N Onozato
  JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, Volume：12, Number：3, First page：199, Last page：202, Mar. 2001, [Reviewed], [Lead, Corresponding]
  The phase diagram of the La2O3-Ta2O5-Ga2O3 system around La3Ta0.5Ga5.5O14 (LTG) was investigated by a differential thermal analysis and the quenching method. La3Ta0.5Ga5.5O14 single crystals were subsequently grown from different starting melt compositions using the Czochralski technique. The effect of the starting melt composition on crystal quality was examined by measuring the variation in the chemical composition and lattice parameters along the growth axis. On the basis of these experimental results, we have grown LTG single crystals over 2 inches in diameter. (C) 2001 Kluwer Academic Publishers.
  KLUWER ACADEMIC PUBL, English, Scientific journal
  DOI：https://doi.org/10.1023/A:1011243219013
  DOI ID：10.1023/A:1011243219013, ISSN：0957-4522, ORCID：47804564, Web of Science ID：WOS:000168886100011
• Formation mechanism and synthesis of apatite-type structure Ba_2+xLa_8-x(SiO₄)₆O_2-d　　　　　　　　　　　　　　　
  H Takeda; M Ohgaki; T Kizuki; K Hashimoto; Y Toda; S Udagawa; K Yamashita
  JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Volume：83, Number：11, First page：2884, Last page：2886, Nov. 2000, [Reviewed], [Lead, Corresponding]
  The formation process of Ba2La8(SiO4)(6)O-2 was clarified using thermogravimetry-differential thermal analysis (TG-DTA) and a high-temperature powder X-rag diffraction (HT-XRD) method, Phase changes identified from the HT-XRD data surprisingly corresponded to the weight loss and/or endothermic peaks observed in the TG-DTA curves. Raw material with the composition Ba2La8(SiO4)(6)O-2 was completely reacted at 1400 degreesC and produced only an apatite-type compound without a secondary phase. Moreover, the synthesis of Ba2+xLa8-x-(SiO4)(6)O2-delta crystals with x = 0-2 was attempted using a solid-state reaction.
  AMER CERAMIC SOC, English, Scientific journal
  DOI：https://doi.org/10.1111/j.1151-2916.2000.tb01654.x
  DOI ID：10.1111/j.1151-2916.2000.tb01654.x, ISSN：0002-7820, ORCID：47804569, Web of Science ID：WOS:000165235600046
• Crystal growth and structure analysis of Sm_2-xCe_xCuO₄　　　　　　　　　　　　　　　
  H Takeda; M Okuno; M Ohgaki; K Yamashita; T Matsumoto
  JOURNAL OF MATERIALS RESEARCH, Volume：15, Number：9, First page：1905, Last page：1910, Sep. 2000, [Reviewed], [Lead, Corresponding]
  The phase diagram of the Sm2O3-CuO system was investigated by the combination of the differential thermal analysis and the quench method. The results showed that Sm2CuO4 incongruently melts at about 1220 degrees C, and that the solid Sm2CuO4 exists in equilibrium with the liquid consisting of 81-95 mol% CuO in the range of 1060-1220 degrees C. On the basis of the phase diagram, Sm2-xCexCuO4 single crystals were grown by the traveling solvent floating zone method. The crystal structure [space group I4/mmm, a = 3.917(1), c = 11.899(2) Angstrom] has been refined using single-crystal x-ray diffraction data with a precision corresponding to an R index of 0.02.
  MATERIALS RESEARCH SOCIETY, English, Scientific journal
  DOI：https://doi.org/10.1557/JMR.2000.0276
  DOI ID：10.1557/JMR.2000.0276, ISSN：0884-2914, ORCID：47804567, Web of Science ID：WOS:000089112800010
• HOMO- AND HETERO- CRYSTAL GROWTH PHENOMENA ON ELECTRICALLY POLED HYDROXYAPATITE CERAMIC SURFACES
  Takeda Hiroaki; Nakamura Satoshi; Yamashita Kimihiro
  Phosphorus Research Bulletin, Volume：11, First page：7, Last page：12, May 2000, [Reviewed], [Lead, Corresponding]
  DOI：https://doi.org/10.3363/prb1992.11.0_7
  DOI ID：10.3363/prb1992.11.0_7, ORCID：47804570
• Dielectric properties of poled hydroxyapatite ceramics　　　　　　　　　　　　　　　
  H Takeda; S Nakamura; K Yamada; T Tsuchiya; K Yamashita
  Key Engineering Materials, Volume：181-182, First page：35, Last page：38, May 2000, [Reviewed], [Lead, Corresponding]
  Dielectric properties of hydroxyapatite (HAp) ceramics have been investigated. Dielectric constants, P-E hysteresis and electric resistance of HAp ceramics were characterized. The thermally stimulated depolarization current (ITSDC) was measured using HAp ceramics polarized under de fields of 1-5kV.cm(-1) at 300-500 degreesC for Ih. The remnant electric charge of poled HAp ceramics was calculated and compared with those of BaTiO3. The results of TSDC measurement suggested that OH- in HAp dissociated into oxygen and hydrogen ions by polarization treatment.
  TRANS TECH PUBLICATIONS LTD, English, Scientific journal
  DOI：https://doi.org/10.4028/www.scientific.net/KEM.181-182.35
  DOI ID：10.4028/www.scientific.net/KEM.181-182.35, ISSN：1013-9826, ORCID：47804568, Web of Science ID：WOS:000165526800009
• Synthesis and characterization of Sr₃TaGa₃Si₂O₁₄ single crystals　　　　　　　　　　　　　　　
  H Takeda; J Sato; T Kato; K Kawasaki; H Morikoshi; K Shimamura; T Fukuda
  MATERIALS RESEARCH BULLETIN, Volume：35, Number：2, First page：245, Last page：252, Jan. 2000, [Reviewed], [Lead, Corresponding]
  New piezoelectric Sr(3)TaGa(3)Si(2)O(14) (STGS) single crystals were grown using the Czochralski technique. The crystal structure of STGS is isostructural to that of Ca(3)Ga(2)Ge(4)O(14), which has the trigonal space group P321 and Z = 1. The lattice parameters were a = 8.293(2) and c = 5.078(2) Angstrom. The final R-factors were R = 0.047 and R(w) = 0.046 for 1406 unique reflections. The distribution of each cation was found to be ordered in each site. Some piezoelectric properties of STGS are reported. (C) 2000 Elsevier Science Ltd. All rights reserved.
  PERGAMON-ELSEVIER SCIENCE LTD, English, Scientific journal
  DOI：https://doi.org/10.1016/S0025-5408(00)00201-4
  DOI ID：10.1016/S0025-5408(00)00201-4, ISSN：0025-5408, ORCID：47804571, Web of Science ID：WOS:000087423700011
• Electrovectorial Effect of Poled Bioceramics on Dissolution and Crystallization　　　　　　　　　　　　　　　
  Takeda Hiroaki; Yamashita Kimihiro
  Transactions of the Materials Research Society of Japan, Volume：25, Number：1, First page：173, Last page：176, Jan. 2000, [Reviewed], [Lead, Corresponding]
  ORCID：49173956
• Synthesis and structure of La₃(M_1/3Ga_2/3)Ga₅O₁₄ (M = Mo⁶⁺ and W⁶⁺) crystals　　　　　　　　　　　　　　　
  H Takeda; J Sato; H Morikoshi; T Kato; K Shimamura; T Fukuda
  MATERIALS LETTERS, Volume：41, Number：3, First page：104, Last page：111, Nov. 1999, [Reviewed], [Lead, Corresponding]
  New Ca3Ga2Ge4O14-type crystals, La-3(M1/3Ga2/3)Ga(5)O(14)d (M = Mo6+ and W6+; LMG and LWG) were synthesized by the solid state reaction and grown using the micro-pulling down (mu-PD) method. The mu-PD growth of these two compounds showed that the crystals melt incongruently. The structure of these crystals has been refined using single-crystal X-ray diffraction data. Mo and W atoms were found to be ordered in the octahedral site coordinated by six oxygen atoms. (C) 1999 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/S0167-577X(99)00112-3
  DOI ID：10.1016/S0167-577X(99)00112-3, ISSN：0167-577X, ORCID：47804578, Web of Science ID：WOS:000083653300003
• Crystal growth of oxide and fluoride materials for optical, piezoelectric and other applications　　　　　　　　　　　　　　　
  T Fukuda; K Shimamura; VV Kochurikhin; VI Chani; BM Epelbaum; SL Baldochi; H Takeda; A Yoshikawa
  JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, Volume：10, Number：8, First page：571, Last page：580, Nov. 1999, [Reviewed]
  High quality oxide and fluoride single crystals for optical, piezoelectric and other applications have been grown by advanced crystal growth techniques. La3Nb0.5Ga5.5O14 and La3Ta0.5Ga5.5O14 piezoelectric single crystals of size and quality comparable to La3Ga5SiO14 (langasite), have been produced. The piezoelectric and device properties of the crystals were investigated. A search for new langasite-type materials was also performed. Growth conditions of (La,Sr)(Al,Ta)O-3 and Ca8La2(PO4)(6)O-2 single crystals are discussed. These crystals have excellent lattice matching with GaN, a promising material for optoelectronic devices. Promising optical micro-crystals-K3Li2Nb5O15, KNbO3 and Y3Al5O12-and new structural materials, Al2O3/Y3Al5O12 eutectic fibers, have been grown by the micro-pulling-down (mu-PD) technique. The advantages of the mu-PD technique have been shown. Ce-doped fluoride single crystals-LiCaAlF6, LiYF4 and BaLiF3-have been grown for solid state UV laser applications. Growth results and optical characterizations are discussed.
  KLUWER ACADEMIC PUBL, English, Scientific journal
  DOI：https://doi.org/10.1023/A:1008933507409
  DOI ID：10.1023/A:1008933507409, ISSN：0957-4522, ORCID：47804573, Web of Science ID：WOS:000083599000003
• Effect of starting melt composition on crystal growth of La₃Nb_0.5Ga_5.5O₁₄　　　　　　　　　　　　　　　
  H Takeda; K Shimamura; VI Chani; T Kato; T Fukuda
  CRYSTAL RESEARCH AND TECHNOLOGY, Volume：34, Number：9, First page：1141, Last page：1147, Oct. 1999, [Reviewed], [Lead, Corresponding]
  Single crystals of La3Nb0.5Ga5.5O14 were grown from different starting melt compositions by the Czochralski technique. The effect of the melt composition on crystal quality was examined by measuring the variation of chemical composition and lattice parameters along the growth axis. The existence of a solid solution range of La3Nb0.5Ga5.5O14 is discussed using X-ray crystal structure analysis.
  WILEY-V C H VERLAG GMBH, English, Scientific journal
  DOI：https://doi.org/10.1002/(SICI)1521-4079(199911)34:9<1141::AID-CRAT1141>3.0.CO;2-W
  DOI ID：10.1002/(SICI)1521-4079(199911)34:9<1141::AID-CRAT1141>3.0.CO;2-W, ISSN：0232-1300, ORCID：47804576, Web of Science ID：WOS:000083814500004
• Effect of (Sr, Ba) substitution in La₃Ga₅SiO₁₄ and La₃M_0.5Ga_5.5O₁₄ (M = Nb⁵⁺, Ta⁵⁺) crystals on their synthesis, structure and piezoelectricity　　　　　　　　　　　　　　　
  H Takeda; T Kato; Chani, VI; H Morikoshi; K Shimamura; T Fukuda
  JOURNAL OF ALLOYS AND COMPOUNDS, Volume：290, Number：1-2, First page：79, Last page：84, Aug. 1999, [Reviewed], [Lead, Corresponding]
  Alkali-earth ion (Sr, Ba) substituted La3Ga5SiO14, and La(3)M(0.5)G(5.5)O(14) (M=Nb5+,Ta5+) compounds were synthesized by solid state reaction. Sr-substituted La3Ta0.5Ga5.5O14 (Sr-LTG) single crystals were grown by the micro-pulling down and Czochralski techniques. The cation distribution in Sr-LTG has been determined by X-ray structure analysis. Some piezoelectric properties of Sr-LTG crystal are reported and compared with those of pure La3Ta0.5Ga5.5O14. (C) 1999 Elsevier Science S.A. All rights reserved.
  ELSEVIER SCIENCE SA, English, Scientific journal
  DOI：https://doi.org/10.1016/S0925-8388(99)00203-0
  DOI ID：10.1016/S0925-8388(99)00203-0, ISSN：0925-8388, ORCID：47804574, Web of Science ID：WOS:000082380800016
• Crystal growth and structure of La₃M⁴⁺Ga₅O₁₄ (M=Ti, Zr, Hf)　　　　　　　　　　　　　　　
  H Takeda; T Kato; VI Chani; K Shimamura; T Fukuda
  JOURNAL OF ALLOYS AND COMPOUNDS, Volume：290, Number：1-2, First page：244, Last page：249, Aug. 1999, [Reviewed], [Lead, Corresponding]
  La(3)M(4+)Ga(5)O(14) (M=Ti, Zr, Hf) compounds were crystallized using the micro-pulling down and Czochralski techniques. Both growth methods showed that these three crystals are peritectic compounds. The structure of La(3)TiGa(5)O(14) (LTiG) crystal was refined using single-crystal X-ray diffraction data. LTiG was observed to be isostructural to Ca(3)Ga(2)Ge(4)O(14) (P321 (No.150), Z=1) and the lattice parameters are a=8.223(1), c=5.109(1) Angstrom. The Ti atoms were found to occupy octahedral (1a) and tetrahedral (3f) sites coordinated by six and four oxygen atoms, respectively. (C) 1999 Elsevier Science S.A. All rights reserved.
  ELSEVIER SCIENCE SA, English, Scientific journal
  DOI：https://doi.org/10.1016/S0925-8388(99)00194-2
  DOI ID：10.1016/S0925-8388(99)00194-2, ISSN：0925-8388, ORCID：47804572, Web of Science ID：WOS:000082380800040
• New oxide crystals as substrate for GaN-based blue light emitting devices　　　　　　　　　　　　　　　
  Tsuguo Fukuda; Kiyoshi Shimamura; T. Tabata; Hiroaki Takeda; N. Futagawa; Akira Yoshikawa; Vladimir V. Kochurikhin
  Journal of Korean Association of Crystal Growth, Volume：9, Number：5, First page：470, Last page：474, Jun. 1999, [Reviewed]
• Liquid phase epitaxy of films with langasite structure　　　　　　　　　　　　　　　
  VI Chani; H Takeda; T Fukuda
  MATERIALS SCIENCE AND ENGINEERING B-SOLID STATE MATERIALS FOR ADVANCED TECHNOLOGY, Volume：60, Number：3, First page：212, Last page：216, Jun. 1999, [Reviewed]
  Epitaxial films of Na2CaGe6O14 with langasite structure were deposited by liquid phase epitaxy (LPE) technique on isomorphic Nd3Ga5SiO14 substrates at a growth temperature of about 1000 degrees C using K2O-V2O5 based flux. The films were about 100 mu m in thickness and had rough surface morphology. The film composition measurements were made by scanning electron-probe microanalysis (EPMA). EPMA data indicated low content of flux forming: K+ and V5+ cations in the films grown. Ca2+ enrichment and Na+ decrease were detected in the vicinity of film/substrate interfaces. (C) 1999 Elsevier Science S.A. All rights reserved.
  ELSEVIER SCIENCE SA, English, Scientific journal
  DOI：https://doi.org/10.1016/S0921-5107(99)00141-5
  DOI ID：10.1016/S0921-5107(99)00141-5, ISSN：0921-5107, ORCID：47804577, Web of Science ID：WOS:000081345900010
• Effect of starting melt composition on crystal growth of La₃Ga₅SiO₁₄　　　　　　　　　　　　　　　
  H Takeda; K Shimamura; VI. Chani; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：197, Number：1-2, First page：204, Last page：209, Feb. 1999, [Reviewed], [Lead, Corresponding]
  The phase diagram of the La2O3-Ga2O3-SiO2 system around La3Ga5SiO14 was investigated by a different thermal analysis and the quenching method. On the basis of this diagram, single crystals of La3Ga5SiO14 were grown from different starting melt compositions by the Czochralski technique. The effect of starting melt composition on crystal quality was examined by measuring the variation of chemical composition and lattice parameters along the growth axis. The congruency and the existence of a solid solution range of La3Ga5SiO14 are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/S0022-0248(98)00814-8
  DOI ID：10.1016/S0022-0248(98)00814-8, ISSN：0022-0248, ORCID：47804575, Web of Science ID：WOS:000078355300030
• Application of spectral analysis for crystal shape improvement during czochralski growth of oxide crystals　　　　　　　　　　　　　　　
  VV Kochurikhin; K Shimamura; BM Epelbaum; H Takeda; T Fukuda
  CRYSTAL RESEARCH AND TECHNOLOGY, Volume：33, Number：1, First page：65, Last page：70, Dec. 1998, [Reviewed]
  The automatic diameter control system using the results of spectral analysis of weight sensor data as a criterion for the amount of feedback tuning was applied successfully for the growth of La3Ga5SiO14 Single crystals. The developed method enabled to determine timely the appearance of oscillations in the control system and to adapt the amplification factor automatically for the maintenance of stable crystal shape. Furthermore, the developed system made it possible to estimate the formation of a second phase at a very early stage.
  WILEY-V C H VERLAG GMBH, English, Scientific journal
  DOI：https://doi.org/10.1002/(SICI)1521-4079(1998)33:1<65::AID-CRAT65>3.0.CO;2-S
  DOI ID：10.1002/(SICI)1521-4079(1998)33:1<65::AID-CRAT65>3.0.CO;2-S, ISSN：0232-1300, ORCID：47804583, Web of Science ID：WOS:000071885600008
• Growth of Gd-Yb-Ga garnet single crystals with large lattice parameters as substrates for optical isolators　　　　　　　　　　　　　　　
  K Shimamura; VV Kochurikhin; H Takeda; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：194, Number：2, First page：203, Last page：208, Nov. 1998, [Reviewed]
  We have successfully grown Gd3YbxGa5-xO12 (GYGG) single crystals by the Czochralski method. The variation in lattice parameter is discussed in relation to the selective site occupancy by the constituent cations of GYGG. Since GYGG single crystals have lattice parameters larger than 12.6 Angstrom, they are promising as new substrates for the growth of iron garnet epitaxial films with high Bi3+ ion concentrations. (C) 1998 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/S0022-0248(98)00689-7
  DOI ID：10.1016/S0022-0248(98)00689-7, ISSN：0022-0248, ORCID：47804582, Web of Science ID：WOS:000077077400007
• Growth and characterization of (La,Sr)(Al,Ta)O₃ single crystals as substrates for GaN epitaxial growth　　　　　　　　　　　　　　　
  K Shimamura; H Tabata; H Takeda; VV Kochurikhin; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：194, Number：2, First page：209, Last page：213, Nov. 1998, [Reviewed]
  We have successfully grown [111] oriented (La,Sr)(Al,Ta)O-3 (LSAT) mixed-perovskite single crystals by the Czochralski method. Compositional uniformity and coloring phenomena are discussed in relation to the growth conditions. Since LSAT single crystals have excellent lattice matching with GaN, they are promising as new substrates for the growth of high-quality GaN epitaxial layers. (C) 1998 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/S0022-0248(98)00730-1
  DOI ID：10.1016/S0022-0248(98)00730-1, ISSN：0022-0248, ORCID：47804580, Web of Science ID：WOS:000077077400008
• Czochralski growth of RE₃Ga₅SiO₁₄ (RE = La, Pr, Nd) single crystals for the analysis of the influence of rare earth substitution on piezoelectricity　　　　　　　　　　　　　　　
  J Sato; H Takeda; H Morikoshi; K Shimamura; P Rudolph; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：191, Number：4, First page：746, Last page：753, Aug. 1998, [Reviewed]
  Pr3Ga5SiO14 and Nd3Ga5SiO14 single crystals with constant diameter of 22 mm and lengths up to 145 mm have been grown by the Czochralski method, The phase identification, site occupancy of cations and axial lattice parameter distribution were determined by X-ray analysis. The transmission spectra within the 340-3200 nm wavelength region were measured, The centre of interest are the piezoelectric properties of (2 (1) over bar 0) and (0 1 0) plates in comparison with former grown La3Ga5SiO14 crystals in order to find out the influence of the rare earth substitution of La3+ by Pr3+ and Nd3+ on the piezoelectric strain constant d(11). A decrease of /d(11)/ with increasing atomic number was found giving the hint to the substitution of lanthanum by further elements with larger atomic radii, (C) 1998 Elsevier Science B.V. All rights reserved.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/S0022-0248(98)00362-5
  DOI ID：10.1016/S0022-0248(98)00362-5, ISSN：0022-0248, eISSN：1873-5002, ORCID：47804579, Web of Science ID：WOS:000075688600022
• Growth and characterization of La₃Ta_0.5Ga_5.5O₁₄ single crystals　　　　　　　　　　　　　　　
  H Kawanaka; H Takeda; K Shimamura; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：183, Number：1-2, First page：274, Last page：277, Jan. 1998, [Reviewed]
  We have grown colorless La3Ta0.5Ga5.5O14 (LTG) single crystals with dimensions of 1 in. in diameter, using the Czochralski technique. The coloration of the crystals reported depends on the growth atmosphere. Piezoelectric properties of LTG crystals were investigated. LTG single crystals showed superior properties for piezoelectric applications.
  ELSEVIER SCIENCE BV, English
  DOI：https://doi.org/10.1016/S0022-0248(97)00481-8
  DOI ID：10.1016/S0022-0248(97)00481-8, ISSN：0022-0248, ORCID：47804581, Web of Science ID：WOS:000071255000035
• Crystal growth and structural characterization of new piezoelectric material La₃Ta_0.5Ga_5.5O₁₄　　　　　　　　　　　　　　　
  H. Takeda; K. Sugiyama; K. Inaba; K. Shimamura; T. Fukuda
  Japanese Journal of Applied Physics Part 2-Letters, Volume：36, Number：7B, First page：L919, Last page：L921, Jul. 1997, [Reviewed], [Lead, Corresponding]
  Scientific journal
  DOI：https://doi.org/10.1143/JJAP.36.L919
  DOI ID：10.1143/JJAP.36.L919, ORCID：47804584, Web of Science ID：WOS:A1997XM98300009
• Growth and characterization of Na₂CaGe₆O₁₄ single crystals　　　　　　　　　　　　　　　
  H Takeda; R Uecker; M Kumatoriya; K Shimamura; P Reiche; T Fukuda
  CRYSTAL RESEARCH AND TECHNOLOGY, Volume：32, Number：7, First page：939, Last page：945, Jul. 1997, [Reviewed], [Lead, Corresponding]
  Transparent, crack-free Na2CaGe6O14 (NCG) single crystals were successfully grown using the Czochralski technique. The largest crystal had 30 mm in total length and 18 mm in maximal diameter. Best crystal quality was achieved under low temperature gradient arrangement. The crystal structure of NCG has been refined from single crystal X-ray diffraction data. Some piezoelectric proper ties of NCG are reported.
  AKADEMIE VERLAG GMBH, English, Scientific journal
  DOI：https://doi.org/10.1002/crat.2170320707
  DOI ID：10.1002/crat.2170320707, ISSN：0232-1300, ORCID：47804585, Web of Science ID：WOS:A1997YK40600006
• Growth and characterization of La₃Nb_0.5Ga_5.5O₁₄ single crystals　　　　　　　　　　　　　　　
  H Takeda; K Shimamura; T Kohno; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：169, Number：3, First page：503, Last page：508, Dec. 1996, [Reviewed], [Lead, Corresponding]
  We have successfully grown piezoelectric La3Nb0.5Ga5.5O14 (LNG) single crystals with dimensions of 1 and 2 inches in diameter, using the Czochralski technique. The congruency of LNG was examined by measuring the lattice parameters and chemical composition of the grown crystals. Device properties of LNG filters were investigated. LNG single crystals showed superior properties for piezoelectric applications.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/S0022-0248(96)00435-6
  DOI ID：10.1016/S0022-0248(96)00435-6, ISSN：0022-0248, ORCID：47804586, Web of Science ID：WOS:A1996VZ79000015
• Growth and characterization of lanthanum gallium silicate La₃Ga₅SiO₁₄ single crystals for piezoelectric applications　　　　　　　　　　　　　　　
  K Shimamura; H Takeda; T Kohno; T Fukuda
  JOURNAL OF CRYSTAL GROWTH, Volume：163, Number：4, First page：388, Last page：392, Jun. 1996, [Reviewed]
  We have successfully grown a new piezoelectric La3Ga5SiO14 (LGS) single crystal, with dimensions of 1 or 2 inch in diameter, using the Czochratski technique. Coloring of the grown crystals was discussed. The device properties of LGS resonators and filters were demonstrated. The LGS single crystal showed superior properties for piezoelectric applications.
  ELSEVIER SCIENCE BV, English, Scientific journal
  DOI：https://doi.org/10.1016/0022-0248(95)01002-5
  DOI ID：10.1016/0022-0248(95)01002-5, ISSN：0022-0248, ORCID：47804587, Web of Science ID：WOS:A1996UW51100007
• 新圧電結晶ランガサイト
  福田承生; 島村清史; 光野卓也; 武田博明; 佐藤充
  Volume：22, Number：5, First page：358, Last page：363, 1995, [Reviewed]
  DOI：https://doi.org/10.19009/jjacg.22.5_358
  DOI ID：10.19009/jjacg.22.5_358, ORCID：47804588

• Control of thermophysical properties of La₃Ta_0.5Ga_5.5O₁₄ crystal by Sr substitution　　　　　　　　　　　　　　　
  武田博明; 蕎麦田雄大; 臼井晴紀; 徳田誠; 杉山和正; 小玉翔平; 柳瀬郁夫; 保科拓也; 鶴見敬章; VILLORA Encarnacion G.; 島村清史
  結晶成長国内会議予稿集(CD-ROM), Volume：50th, 2021
  ISSN：0385-6275, J-Global ID：202202222663219101
• Effect of element substitution on thermophysical properties of langasite-type crystal　　　　　　　　　　　　　　　
  臼井晴紀; 徳田誠; 保科拓也; 鶴見敬章; 杉山和正; LEBBOU Kheirreddine; 武田博明
  日本セラミックス協会年会講演予稿集(CD-ROM), Volume：2020, 2020
  J-Global ID：202002279944019417
• 四成分系ランガサイト型結晶の構造と物性　　　　　　　　　　　　　　　
  武田博明; 臼井晴紀; 保科拓也; 鶴見敬章; 杉山和正; 徳田誠
  Volume：2019, 2019
  J-Global ID：202002252628576978
• Structural changes on russellite by HCl treatment　　　　　　　　　　　　　　　
  Sakai Yuka; Okudera Hiroki; Arasuna Akane; Takeda Hiroaki
  Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences, Volume：2017, First page：87, 2017
  By comparing structures of russellite before and after HCl treatment we found shrinkage of b, relaxations in tilt of WO₆ octahedra and shift of W along -c within one of O₄ squares normal to b. Change in IR spectra suggested that HCl treatment straighten the O-W-O sequence without changing the distance of diagonal oxygen atoms, in harmony with the X-ray result. Presence of water-attributable absorption band indicate presence of physisorption sites on the surface of powdery specimen.
  Japan Association of Mineralogical Sciences, Japanese
  DOI：https://doi.org/10.14824/jakoka.2017.0_87
  DOI ID：10.14824/jakoka.2017.0_87, CiNii Articles ID：130007785958
• ゲーレナイトの圧電材料としての可能性 (特集 GRENE振動発電用鉛フリー圧電体開発の概要)　　　　　　　　　　　　　　　
  武田 博明; 保科 拓也; 鶴見 敬章; 小玉 展宏; 萩原 学; 藤原 忍
  Volume：47, First page：11, Last page：15, Nov. 2016
  Japanese
  ISSN：0285-3833, CiNii Articles ID：40021386477, CiNii Books ID：AN00330126
• Dielectric Breakdown Mechanism and Its Temperature Dependence of Ceramic Dielectrics　　　　　　　　　　　　　　　
  鶴見 敬章; 山崎 幹雄; 保科 拓也; 武田 博明
  Volume：51, Number：10, First page：666, Last page：670, Oct. 2016
  Japanese
  ISSN：0009-031X, CiNii Articles ID：40021187510, CiNii Books ID：AN00131516
• Problems and Future of Lead-free Piezoelectric Materials　　　　　　　　　　　　　　　
  鶴見 敬章; 保科 拓也; 武田 博明
  Volume：24, Number：12, First page：62, Last page：72, Dec. 2011
  Japanese
  ISSN：1344-7858, CiNii Articles ID：40019149100, CiNii Books ID：AA11323801
• Crystal Growth of High Temperature Piezoelectric Crystals from Quasi-Congruent Melt　　　　　　　　　　　　　　　
  TAKEDA Hiroaki; TSURUMI Takaaki
  Ceramics Japan, Volume：46, Number：8, First page：657, Last page：661, 01 Aug. 2011
  Japanese
  ISSN：0009-031X, CiNii Articles ID：10030200563, CiNii Books ID：AN00131516
• 27pTM-3 High-temperature X-ray diffraction study of Bi_2WO_6　　　　　　　　　　　　　　　
  Yoneda Yasuhiro; Kohara Shinji; Han Joong Sang; Takeda Hiroaki; Tsurumi Takaaki
  Meeting abstracts of the Physical Society of Japan, Volume：66, Number：1, First page：982, Last page：982, 03 Mar. 2011
  The Physical Society of Japan (JPS), Japanese
  ISSN：1342-8349, CiNii Articles ID：110008715801, CiNii Books ID：AA11439205
• Influence of Interface on Tunability in Barium Strontium Titanate
  Naohiro Horiuchi; Takuya Hoshina; Hiroaki Takeda; Takaaki Tsurumi
  Ceramic Transactions Series, First page：37, Last page：42, 28 Jun. 2010
  Wiley
  DOI：https://doi.org/10.1002/9780470909850.ch4
  DOI ID：10.1002/9780470909850.ch4, eISSN：2637-4390
• Search for Piezoelectric Single Crystals for Sensing Applications at Elevated Temperatures　　　　　　　　　　　　　　　
  TAKEDA Hiroaki; TSURUMI Takaaki
  Ceramics Japan, Volume：45, Number：6, First page：474, Last page：478, 01 Jun. 2010
  Japanese
  ISSN：0009-031X, CiNii Articles ID：10026877799, CiNii Books ID：AN00131516
• 25aYJ-6 Dielectric and Piezoelectric Properties of Fine-grained Barium Titanate Ceramics　　　　　　　　　　　　　　　
  Hoshina Takuya; Kigoshi Yoichi; Hatta Saki; Takeda Hiroaki; Tsurumi Takaaki
  Meeting abstracts of the Physical Society of Japan, Volume：64, Number：2, First page：853, Last page：853, 18 Aug. 2009
  The Physical Society of Japan (JPS), Japanese
  ISSN：1342-8349, CiNii Articles ID：110007499127, CiNii Books ID：AA11439205
• Synthesis and characterization of (Bi1/2A1/2)- modified BaTiO3 (A=Na, K) semiconducting ceramics　　　　　　　　　　　　　　　
  H. Takeda; T. Hoshina; T. Tsurumi; T. Shiosaki; P. H. Xiang
  5th IMAPS/ACerS International Conference and Exhibition on Ceramic Interconnect and Ceramic Microsystems Technologies 2009, CICMT 2009, First page：183, Last page：187, 2009
  The electric properties of BaTiO3-(Bi1/ 2A1/2)TiO3 (A=Na, K) solid solution ceramics were studied as a lead-free PTCR (positive temperature coefficient of resistivity) thermistor material usable over 130°C. For determining the maximum switching temperature Ts, the phase diagrams of BaTiO 3-(Bi1/2Na1/2)TiO 3 (BT-BNT) and BaTiO3-(Bi1/2K1/ 2)TiO3 (BT-BKT) binary system were clarified. We obtained lead-free PTC materials with a low resistivity at room temperature (PRT) and high temperature coefficient (a) by sintering the ceramics in a low O 2 containing atmosphere.
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84879866709&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84879866709&origin=inward
  SCOPUS ID：84879866709
• Size effect and domain contribution in barium titanate　　　　　　　　　　　　　　　
  Takaaki Tsurumi; Takuya Hoshina; Hiroaki Takeda
  5th IMAPS/ACerS International Conference and Exhibition on Ceramic Interconnect and Ceramic Microsystems Technologies 2009, CICMT 2009, First page：112, Last page：115, 2009
  Barium titanate (BaTiO3) ceramics with various grain sizes were prepared by a conventional sintering method and a two-step sintering method. The permittivity of the ceramics increased with decreasing the grain size down to 1.1 μm on average. The BaTiO3 ceramics with an average grain size of 1.1 μm had a high permittivity of 7,700. The transmission electron microscopy (TEM) observation revealed that the 90° domain density increased with decreasing the grain size. From an ultra wide range dielectric spectroscopy, it was found that the high domain density enhanced the orientational polarizability due to the domain-wall vibration and the ionic polarizability due to the lattice vibration. It was clarified that the increase of the permittivity with decreasing the grain size was due to the domain size effect.
  Scopus：https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84879867968&origin=inward
  Scopus Citedby：https://www.scopus.com/inward/citedby.uri?partnerID=HzOxMe3b&scp=84879867968&origin=inward
  SCOPUS ID：84879867968
• 圧電・超音波材料 希土類Caボレート単結晶の作製と圧電特性--LaCa4O(BO3)3系単結晶の作製と材料定数決定と弾性表面波特性　　　　　　　　　　　　　　　
  塩嵜 忠; 清水 寛之; 武田 博明
  Volume：18, Number：4, First page：6, Last page：10,126, Jul. 2006
  Japanese
  ISSN：0916-2410, CiNii Articles ID：40007411555, CiNii Books ID：AN10068970
• P1-2 Evaluation of Piezoelectric Constants of GdCOB Crystal and Calculation of Their SAW Characteristics　　　　　　　　　　　　　　　
  Nishida Takashi; Shimizu Hiroyuki; Takeda Hiroaki; Uchiyama Kiyoshi; Shiosaki Tadashi
  Proceedings of Symposium on Ultrasonic Electronics, Volume：26, First page：41, Last page：42, 16 Nov. 2005
  Steering committee of symposium on ultrasonic electronics, Japanese
  ISSN：1348-8236, CiNii Articles ID：110007458540, CiNii Books ID：AA1240726X
• P1-3 Piezoelectric, elastic and dielectric constants and SAW properties of RCa_4O(BO_3)_3(R=La,Gd,Y) single crystals　　　　　　　　　　　　　　　
  Kondo Ayako; Shimizu Hiroyuki; Nishida Takashi; Takeda Hiroaki; Uchiyama Kiyoshi; Shiosaki Tadashi
  Proceedings of Symposium on Ultrasonic Electronics, Volume：26, First page：43, Last page：44, 16 Nov. 2005
  Steering committee of symposium on ultrasonic electronics, Japanese
  ISSN：1348-8236, CiNii Articles ID：110007458541, CiNii Books ID：AA1240726X
• P2-19 Evaluation of material constants and SAW properties in LaCa_4O(BO_3)_3 single crystal(Short presentation for poster)　　　　　　　　　　　　　　　
  Shimizu Hiroyuki; Takeda Hiroaki; Nishida Takashi; Shikida Takashi; Okamura Soichiro; Shiosaki Tadashi
  Proceedings of Symposium on Ultrasonic Electronics, Volume：25, First page：195, Last page：196, 27 Oct. 2004
  Steering committee of symposium on ultrasonic electronics, Japanese
  ISSN：1348-8236, CiNii Articles ID：110007458381, CiNii Books ID：AA1240726X
• Development of Ca_3Ga_2Ge_4O_<14>-Type Crystals for Piezoelectric Applications　　　　　　　　　　　　　　　
  TAKEDA Hiroaki; SHIMAMURA Kiyoshi; OKAMURA Soichiro; SHIOSAKI Tadashi
  Journal of the Society of Inorganic Materials,Japan, Volume：11, Number：308, First page：43, Last page：49, 01 Jan. 2004
  Japanese
  ISSN：1345-3769, CiNii Articles ID：10012478144, CiNii Books ID：AA11416367
• Development of Rare-earth Elements Based Piezoelectric Materials　　　　　　　　　　　　　　　
  SHIOSAKI Tadashi; TAKEDA Hiroaki; NISHIDA Takashi; OKAMURA Soichiro
  Rare earths., Volume：43, First page：73, Last page：81, 14 Nov. 2003
  Japanese
  ISSN：0910-2205, CiNii Articles ID：10012510478, CiNii Books ID：AN10379697
• Piezoelectric properties and structural characterization of (Na,Bi)Bi2Ta2O9 ceramics with bismuth layer-structure　　　　　　　　　　　　　　　
  R. Aoyagi; M. Matsushita; K. Komagata; H. Takeda; S. Okamura; T. Shiosaki
  IEEE International Symposium on Applications of Ferroelectrics, First page：311, Last page：314, 2002
  The piezoelectric properties of bismuth layer-structured ferroelectrics Nao0-5-xBi0.5+x/3Bi2Ta2O9 (NBT(x)) dense ceramics were investigated, and the crystal structure of synthesized NBT(x) powders was analyzed by the Rietveld method. NBT(x) powder and ceramics were prepared by conventional synthesis method. NBT(x) powder for x=0 and x=0.1 was confirmed to be single phase of BLSFs (m=2) by x-ray diffraction method. The electromechanical coupling coefficients kp of NBT(x=0) and NBT(x=0.1) dense ceramics were 10% and 8.3%, respectively. The kp of NBT(x=0) was one of the largest in reported non-oriented BLSFs ceramics.
  English
  SCOPUS ID：0038608215
• Epitaxial growth of tungsten bronze (Sr,Ba)Nb2O6 thin films by chemical solution deposition　　　　　　　　　　　　　　　
  Rintaro Aoyagi; Hiroaki Takeda; Soichiro Okamura; Takashi Nishida; Tadashi Shiosaki
  IEEE International Symposium on Applications of Ferroelectrics, Volume：2, First page：905, Last page：908, 2000
  Epitaxial growth feature of ferroelectric Sr0.5Ba0.5Nb2O6 (SBN) thin films synthesized by chemical solution deposition was investigated by enhanced XRD analyses. SBN thin films on MgO (100) crystallized to a mixture of end members SrNb2O6 and BaNb2O6 at 700°C (heating rate: 10°C). The sintering at over 1000°C (heating rate: 10°C) or at 700°C (heating rate: 1°C) was necessary in order to obtain the tetragonal tungsten bronze phase SBN. Two crystal lattice planes of (001)- and (310)- oriented SBN were intergrown an orientation of ±18.5° and 0° (90°), respectively.
  English
  SCOPUS ID：0034470441
• Growth and characterization of new substituted langasite-type piezoelectric crystals　　　　　　　　　　　　　　　
  KATO T.; TAKEDA H.; SIMAMURA K.; FUKUDA T.
  Journal of the Japanese Association of Crystal Growth, Volume：25, Number：3, First page：A7, Jul. 1998
  We have developed new substituted langasite crystals in order to increase piezoelectric constants. By solid state reaction and micro-pulling down technique, La_<2.75>Sr_<0.25>Ta_<0.625>Ga_<5.375>O_<14> and Sr_3TaGa_3Si_2O_<14> were obtained as single phase with langasite-type structure. These crystals with bulk size were also grown by the Czochralski technique.
  The Japanese Association for Crystal Growth (JACG), Japanese
  ISSN：0385-6275, CiNii Articles ID：110002715037, CiNii Books ID：AN00188386
• Crystal Growth and Characterization of (La, Sr)(Al, Ta)O_3 Substrate for blue light emitting devices　　　　　　　　　　　　　　　
  TAKEDA H.; TABATA H.; SIMAMURA K.; FUKUDA T.
  Journal of the Japanese Association of Crystal Growth, Volume：25, Number：3, First page：A11, Jul. 1998
  Bulk (La,Sr)(Al.Ta)O_3 single crystals were successfully grown by the Czochralski technique for a substrate material of GaN thin film. The lattice parameter and chemical composition of crystals were constant along the growth direction. Coloring of the grown crystals was discussed.
  The Japanese Association for Crystal Growth (JACG), Japanese
  ISSN：0385-6275, CiNii Articles ID：110002715041, CiNii Books ID：AN00188386
• Crystal Growth and Physical Properties of La_3(Ga_<5-X> 2Al_x)SiO_<14>　　　　　　　　　　　　　　　
  KUMATORIYA M.; TAKEDA H.; SHIMAMURA K.; TAKAGI H.; FUKUDA T.
  Journal of the Japanese Association of Crystal Growth, Volume：24, Number：2, First page：159, Last page：159, 01 Jul. 1997
  Al substituted Langasrte crvstals,La_3(Ga_<5-X> Al_X)Si0_<14>were synthesized by solid phase reaction, μ-pulling down and Czochralski techniques. From the result of solid phase reaction,χ=2.0 was found to be limit of substitution. In χ=0.5 crystal which was grown by Czochralski method, electromechanical coupling coefficients, k_<26>and k_t compared favorably with that of La_3Ga_5Si0<14>
  The Japanese Association for Crystal Growth (JACG), Japanese
  ISSN：0385-6275, CiNii Articles ID：110002714873, CiNii Books ID：AN00188386

• セラミック工学ハンドブック　　　　　　　　　　　　　　　
  2002

• Developent of the real-time remote alpha-ray/gamma-ray/neutron monitor using noble scintillators　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 01 Apr. 2024 - 31 Mar. 2028
  Saitama University
  Grant amount(Total)：18590000, Direct funding：14300000, Indirect funding：4290000
  Grant number：24K01397
• ケイ酸塩系新圧電結晶の結晶構造に基づく材料設計と高温振動子の開発　　　　　　　　　　　　　　　
  01 Apr. 2022 - 31 Mar. 2026
  Grant amount(Total)：17290000, Direct funding：13300000, Indirect funding：3990000
  Grant number：22H02162
• エマージェント物性を生みだす超秩序構造の創出　　　　　　　　　　　　　　　
  19 Nov. 2020 - 31 Mar. 2025
  Grant amount(Total)：175240000, Direct funding：134800000, Indirect funding：40440000
  Grant number：20H05879
• 層状構造等をもつセラミックスを用いた空気中二酸化炭素の室温高速吸収無機固体の創成　　　　　　　　　　　　　　　
  01 Apr. 2021 - 31 Mar. 2024
  Grant amount(Total)：4160000, Direct funding：3200000, Indirect funding：960000
  Grant number：21K05222
• Development of high-performance, safe and low-cost solid energy-storage capacitors　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Challenging Research (Pioneering), 01 Apr. 2020 - 31 Mar. 2023
  Tokyo Institute of Technology
  Grant amount(Total)：26000000, Direct funding：20000000, Indirect funding：6000000
  Grant number：20K20439
• Construction of a terahertz spectroscopic ellipsometer system for ion dynamics analysis　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 01 Apr. 2018 - 31 Mar. 2022
  Hoshina Takuya, Tokyo Institute of Technology
  Grant amount(Total)：17420000, Direct funding：13400000, Indirect funding：4020000
  In this study, a terahertz spectroscopic ellipsometer system was constructed to measure the complex permittivity of inorganic solid materials in the millimeter to terahertz wave band. By analyzing the measured data, we aimed to understand ion dynamics, which is the origin of dielectric properties or ion conductivity. In particular, the order-disorder mode of barium titanate-based ferroelectrics, size effect of the same material system, dielectric polarization mechanism of lead-based relaxor ferroelectrics, and concerted action of ion diffusion and phonons in lithium ion conductors were clarified.
  Grant number：18H01703
• 水晶を凌駕する新規圧電材料・デバイスの開発　　　　　　　　　　　　　　　
  Apr. 2019 - Mar. 2022
  Principal investigator
  Competitive research funding
• Proposal and verification of possibility for solid ion capacitors as an energy storage devise　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), 01 Apr. 2016 - 31 Mar. 2021
  Tsurumi Takaaki, Tokyo Institute of Technology
  Grant amount(Total)：44590000, Direct funding：34300000, Indirect funding：10290000
  The possibility of a solid-state ion capacitor that uses the long-range motion of ions in a solid to generate polarization has been verified as an energy storage device. The discharge amount of the solid ion capacitor using lithium lanthanum oxide as a solid electrolyte increased with due to the specific surface area of the electrode and the electric field applied to the electrolyte. A typical charge / discharge characteristics were also observed in the capacitors using lithium oxide glass as the electrolyte. A thin-layer capacitor was prepared using lithium oxide glass and nickel foil. The new concept of Faraday current barrier has made it possible to significantly improve charge / discharge efficiency and high voltage charge / discharge operation of the capacitor.
  Grant number：16H02394
• Development of new resonator material having a wide temperature range operation and high surface activity　　　　　　　　　　　　　　　
  JSPS, KAKEN: Grant-in-Aid for Scientific Research (B), Apr. 2016 - Mar. 2019
  TAKEDA Hiroaki, Principal investigator
  Grant amount(Total)：16510000, Direct funding：12700000, Indirect funding：3810000
  Competitive research funding
• The development of the high-resistance new single crystal material was directed to a high temperature piezoelectric sensor　　　　　　　　　　　　　　　
  JSPS, KAKEN: Fund for the Promotion of Joint International Research (Fostering Joint International Research), Fund for the Promotion of Joint International Research (Fostering Joint International Research), Apr. 2016 - Mar. 2019
  TAKEDA Hiroaki, Tokyo Institute of Technology, Principal investigator
  Grant amount(Total)：9490000, Direct funding：7300000, Indirect funding：2190000
  In this study, we successfully grew mellilite-type single crystals which have attracted much attention as promising materials for combustion pressure sensor (CPS). Prior to growth experiment, in order to improve the performance of the crystal, we found a relationship between crystal structure, piezoelectricity and mechanical strength in the melilite-type crystals by the first-principles calculation. Based on the result, Sr-substituted gehlenite (SG) single crystal were grown by a Czochralski method. The electromechanical coefficients of the SG crystal were slightly small than those for the pure one, but were sufficient values for application. The mechanical strength of gehlenite increased by a factor of about 1.6 after both Sr substitution and optimization of the crystal substrate orientation. The SG crystal is the most attractive candidate for the CPS use.
  Competitive research funding, Grant number：15KK0201
• Development of piezoelectric crystals with high resistivity for high temperature applications　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), 01 Apr. 2013 - 31 Mar. 2016
  Takeda Hiroaki; TSURUMI Takaaki; HOSHINA Takuya, Tokyo Institute of Technology
  Grant amount(Total)：18070000, Direct funding：13900000, Indirect funding：4170000
  In this study, we report growth and electrical properties of Ca2Al2SiO7 (CAS) and its modified single crystals with melilite-type structure. These crystals showed high chemical stability, stable piezoelectric property, and high resistivity even at high temperature. Moreover, these crystals were easily grown by a conventional bulk growth technology. This study also demonstrated superior combustion sensor performance using these crystals even at 700 degree C. These results suggest that CAS and its modified crystals are the most promising candidate materials for piezoelectric sensor application at high temperatures.
  Grant number：25288104
• Development and Evaluation of Inorganic Electro-optic Crystals Based on a New Theory　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 01 Apr. 2013 - 31 Mar. 2016
  Tsurumi Takaaki; TAKEDA Hiroaki; HOSHINA Takuya, Tokyo Institute of Technology
  Grant amount(Total)：18200000, Direct funding：14000000, Indirect funding：4200000
  This study aimed for developing new lead-free electro-optic (EO) materials with superior performance to lanthanum-added lead zirconate titanate (PLZT). A measuring system of EO-effect was developed for opaque polycrystalline samples prepared by conventional solid state reaction process. Materials studied were pseudo-cubic provskite relaxors. We found that some barium titanate-based relaxors with the composition of barium titanate added with barium zirconate, calcium titanate and barium tin oxide exhibited higher EO-effect than that of PLZT. The EO-coefficients showed a maximum at room temperature and decreased with increasing temperature. The temperature dependence of the EO-coefficients was similar to that of permittivity of these materials.
  Grant number：25289224
• Development of piezoelectric crystals with high resistivity for high temperature applications　　　　　　　　　　　　　　　
  JSPS, KAKEN: Grant-in-Aid for Scientific Research (B), Apr. 2013 - Mar. 2016
  TAKEDA Hiroaki, Principal investigator
  Grant amount(Total)：18070000, Direct funding：13900000, Indirect funding：4170000
  Competitive research funding
• Control and analysis of giant polarization generated by electron migration　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), 2010 - 2012
  TUSUMI Takaaki; TAKEDA Hiroaki; HOSHINA Takuya, Tokyo Institute of Technology
  Grant amount(Total)：18460000, Direct funding：14200000, Indirect funding：4260000
  It is necessary to enhance polarization to obtain new materials with giant dielectric constants. Polarization is given by the product of charge and its displacement. We tried to enhance the polarization using migration of electrons in the artificial structures. Two kind of artificial structures, artificial superlattices with two conductive atomic layers and imhomogenous structure formed by spinodal decomposition, were formed, and found that the electron migration in these artificial structures enhance the polarization, giving rise to an marked increase of dielectric constants. The similar enhancement was observed when the ionic migration in a solid electrolyte was use to generate polarization.
  Grant number：22360269
• The development of environment-friendly lead-free piezoelectric actuator material　　　　　　　　　　　　　　　
  JSPS, KAKEN: Grant-in-Aid for Scientific Research on Priority Areas, Apr. 2007 - Mar. 2009
  TAKEDA Hiroaki, Principal investigator
  Grant amount(Total)：7600000, Direct funding：7600000
  Competitive research funding
• Phonon analysis and crystal chemical simulation of dielectrics based on sub-millimeter wave ellipsometry　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (A), 2007 - 2009
  TSURUMI Takaaki; TAKEDA Hiroaki; HOSHINA Takuya, Tokyo Institute of Technology
  Grant amount(Total)：47450000, Direct funding：36500000, Indirect funding：10950000
  Sub-millimeter wave spectroscopic ellipsometry has been developed to study the size effect of barium titanate and the phase transition behaviors of barium titanate-based relaxors. Ellipsometer is equipment which measures the change of polarizing state of reflected light to determine the complex dielectric permittivity of materials. Accuracy of the ellipsometer developed in this study was verified and the complex permittivity of a barium titanate single crystal was directly determined using it. S for the size effect, the permittivity of barium titanate ceramics increased with decreasing grain size when the grain size was over 1.1μm, while that decreased when the grain size was below 1μm. Most of the domains in BaTiO_3 grains had simple lamellar structures, and 90° domain width decreased with decreasing grain size. Based on wide band dielectric spectroscopy, the domain contribution to the permittivity was investigated. In BaTiO_3 ceramics with grain sizes over 1μm, the dipole and ionic polarizabilities were enhanced by the high domain density. In contrast, for the BaTiO_3 ceramics with grain sizes below 1μm, these polarizabilities were weakened. As for the phase transition of barium titanate-based relaxors, wideband dielectric spectra from kHz to THz were measured for ceramics of BaTiO_3 (BT), Ba_<0.6>Sr_<0.4>TiO_3 (BST-0.6) and BaZr_<0.25>Ti_<0.75>O_3 (BZT-0.25). The behavior in the dipole polarization near the dielectric maximum temperature (T_m) in BST-0.6 and BZT-0.25 could be explained by the behavior in polar nanoregions (PNRs), while the ferroelectric domains contribute to dipole polarization in BT. Relaxation in BT could be interpreted as successive change in polarization behavior from normal ferroelectrics to relaxor ferroelectric via DPT ferroelectrics.
  Grant number：19206068
• Deployment of the synthesis of high temperature corresponding piezoelectric crystal by the solid solubility limit doping and to the combustion pressure sensor element　　　　　　　　　　　　　　　
  JSPS, KAKEN: Grant-in-Aid for Young Scientists (A), Apr. 2005 - Mar. 2008
  TAKEDA Hiroaki, Principal investigator
  Grant amount(Total)：24700000, Direct funding：19000000, Indirect funding：5700000
  Competitive research funding
• Synthesis and evaluation of high-temperature high-Tc aimed the corresponding piezoelectric actuator and high binding ferroelectric single crystal　　　　　　　　　　　　　　　
  JSPS, KAKEN: Grant-in-Aid for Scientific Research on Priority Areas, Apr. 2005 - Mar. 2007
  TAKEDA Hiroaki, Principal investigator
  Grant amount(Total)：4000000, Direct funding：4000000
  Competitive research funding
• Deployment of high-performance piezoelectric material of new bismuth layered oxide ferroelectric　　　　　　　　　　　　　　　
  JSPS, KAKEN: Grant-in-Aid for Young Scientists (B), Apr. 2002 - Mar. 2004
  TAKEDA Hiroaki, Principal investigator
  Grant amount(Total)：3400000, Direct funding：3400000
  Competitive research funding
• Fabrication of Ferroelectric Nanocapacitors by Electron-beam Projection Patterning　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 2003 - 2004
  OKAMURA Soichiro; TAKEDA Hiroaki; NISHIDA Takashi, Nara Institute of Science and Technology
  Grant amount(Total)：3700000, Direct funding：3700000
  A projection lithography technique of electron beam was applied to the fabrication of ferroelectric nanocapacitors to increase throughput. First of all, we tried to fabricate stencil masks. The stencil mask with square holes of 300x300 nm^2 was successfully prepared by using Ti foils with a thickness of 2 μm and etching them by FIB. Well-collimated electron beam was necessary to prevent the broadening pattern size. The distance of 10 μm between the mask and the sample was optimum for preventing undesirable exposure by secondary electrons from the mask. Finally, fine 400x400 nm^2-sized PZT nanocapacitors with self-aligned top Pt electrodes were successfully fabricated by the electron-beam-projection-lithography.
  Parasitic capacitances attended in the measurement of hysteresis properties of ferroelectric microcapacitors were estimated. A scanning probe microscope with a conductive cantilever was used for contacting to various sized PZT capacitors. A parasitic capacitance on condition the cantilever was lifted up by 40 μm from the contact point was estimated to be 0.88 pF. From the capacitor area dependence of the hysteresis slopes, the increase in parasitic capacitance by bringing the cantilever near to substrates for contact was estimated to be 0.061 pF.
  In the second year, we tried to fabricated ferroelectric photonic crystals. Ferroelectric photonic crystals consisted of a PLZT matrix and 800 nm-pitch air-holes with a diameter of 560 nm were successfully fabricated by the electron-beam-induced patterning process. Hexagonal holes inscribed to the circles with a diameter of 400 nm in a precursor matrix changed to circular holes with a diameter of 560 nm after heat-treatment due to shrinkage of the matrix. The optical properties of CSD-derived PLZT films were also evaluated. The PLZT films showed the refractive index of 2.3 and the Kerr constant of 0.4x10^<-16> m^2/V^2. Therefore, it is expected that an applied voltage of 9.7 V to 1 μm-thick PLZT photonic crystals induces 1%-decrease in refractive index and 40^o-swinging of light with a wavelength of 1.55 μm.
  Grant number：15560277
• Development and Characterization of Langasite-type crystals for surface acoustic wave device　　　　　　　　　　　　　　　
  Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 2001 - 2002
  SHINOSAKI Tadashi; TAKEDA Hiroaki; NISHIDA Takashi; OKAMURA Soichiro, NARA INSTITUTE OF SCIENCE AND TECHNOLOGY
  Grant amount(Total)：3000000, Direct funding：3000000
  In this study, we paid attention to Langasite (La_3Ga_5Sio_<14>: LGS) -type crystals. The LGS crystal is a leading material suitable for piezoelectric applications, because the crystal has intermediate properties between those properties of quartz and lithium tantalate (LiTaO_3) in electricity. However, a large amount of expensive gallium oxide as the raw material is necessary for mass-production. The aims of this study are to develop new LGS-type crystals consisting of lower gallium oxides.
  In the first year, we have developed Al substituted LGS crystals (La_3Ga_<5-x>Al_xSiO_<14> (0 of Al in LGS was 1.03 to 1.07 and that the Al solubility limit was x<1.0. A single-crystal x-ray structure analysis reveals that Al atoms are distributed in all cation sites except for the decahedral one occupied by La, by rather favoring the smallest tetrahedral one. The piezoelectric modulus l d_<11> l increased; 1.3% and d_<14> decreased; 7.7% with the increasing Al content, x, up to 1.0. The Al-content obtaining the maximum electromechanical coupling factors (k_<12>, k_<25>, and k_<26>) was x=0.6.
  In the second year, new piezoelectric Ba_3TaGa_3Si_2O_<14> (BTGS) crystal was synthesized by the Czochralski technique using raw materials with stoichiometric compositions. An analysis of growing process showed that the BTGS crystal congruently melts. The crystal structure of BTGS has been refined using single-crystal X-ray diffraction data. The distribution pf each cation was found to be ordered in each site. The maximum electromechanical factors k^2 in Y-cut BTGS wafer was about 0.43% at X-axis propagation. This value was larger than those of LGS.
  For both LGAS and BTGS crystals enables the use of a lower amount of expensive gallium oxide as the raw material. Therefore, we can say that these two crystals are the preferable piezoelectric materials with the Langasite-type structure for both bulk- and surface-acoustic wave devices.
  Grant number：13650346