研究者詳細 - 谷口　博基

Titanite-type solid solutions (Ca,Pb)TiGeO5: a competition between triclinic and antiferroelectric distortions 査読有り

Zerui Li, Taro Kuwano, Akitoshi Nakano, Manabu Hagiwara, Shintaro Yasui, Hiroki Taniguchi, Hiroko Yokota

Journal of the Ceramic Society of Japan advpub 巻 ( 0 ) 2025年

Theoretical and data-driven approaches to semiconductors and dielectrics: from prediction to experiment 査読有り Open Access

Oba F., Nagai T., Katsube R., Mochizuki Y., Tsuji M., Deffrennes G., Hanzawa K., Nakano A., Takahashi A., Terayama K., Tamura R., Hiramatsu H., Nose Y., Taniguchi H.

Science and Technology of Advanced Materials 25 巻 ( 1 ) 頁： 2423600 2024年12月

担当区分：最終著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Science and Technology of Advanced Materials

Computational approaches using theoretical calculations and data scientific methods have become increasingly important in materials science and technology, with the development of relevant methodologies and algorithms, the availability of large materials data, and the enhancement of computer performance. As reviewed herein, we have developed computational methods for the design and prediction of inorganic materials with a particular focus on the exploration of semiconductors and dielectrics. High-throughput first-principles calculations are used to systematically and accurately predict the local atomic and electronic structures of polarons, point defects, surfaces, and interfaces, as well as bulk fundamental properties. Machine learning techniques are utilized to efficiently predict various material properties, construct phase diagrams, and search for materials satisfying target properties. These computational approaches have elucidated the mechanisms behind material functionalities and explored promising materials in combination with synthesis, characterization, and device fabrication. Examples include the development of ternary nitride semiconductors for potential optoelectronic and photovoltaic applications, the exploration of phosphide semiconductors and the optimization of heterointerfaces toward the improvement of phosphide-based photovoltaic cells, and the discovery of ferroelectricity in layered perovskite oxides and the theoretical understanding of its origin, all of which demonstrate the effectiveness of our computer-aided materials research.

DOI： 10.1080/14686996.2024.2423600

Open Access

Re-estimation of Maxwell-Wagner relaxation for novel absorbers via (Ta+Ga)-doped rutile-type TiO2 ceramics with various valence proportions and sintering temperatures 査読有り

High dielectric breakdown strength of antipolar CaTiGeO5 ceramics sintered at optimized temperature 査読有り Open Access

50 巻 ( 18 ) 頁： 34197 - 34204 2024年9月

Effect of Al–Nb codoping on dielectric properties and breakdown strength of rutile TiO2 ceramics 査読有り

Mitsuha Kawasaki, Taro Kuwano, Hiroki Taniguchi, Shinobu Fujihara, Manabu Hagiwara

Journal of the Ceramic Society of Japan 132 巻 ( 7 ) 頁： 304 - 311 2024年7月

Ferroelectric polycrystalline Bi2SiO5 thin films on Pt-covered Si substrates prepared by pulsed laser deposition combined with post-annealing 査読有り

Haruto Takahashi, Shingo Maruyama, Hiroshi Naganuma, Hiroki Taniguchi, Ryota Takahashi, Shintaro Yasui, Kenichi Kaminaga, Yuji Matsumoto

Journal of Alloys and Compounds 988 巻 ( 15 ) 頁： 174195 2024年6月

Antiferroelectricity of titanite-type oxide SrTiGeO5 and its potential for power electronics applications 査読有り

Toshiya Uohashi, Taro Kuwano, Manabu Hagiwara, Kenji Natori, Kazuhiko Deguchi, Hiroki Taniguchi

Applied Physics Letters 124 巻 ( 18 ) 頁： 182901 2024年4月

T. Kuwano, Y. Hashimoto, K. Deguchi, H. Taniguchi

Journal of Alloys and Compounds 966 巻 2023年12月

Dielectric Materials with Hyperordered Structures 査読有り

Hiroki Taniguchi

Hyperordered Structures in Materials: Disorder in Order and Order within Disorder 頁： 313 - 331 2023年10月

Direct microwave energy input on a single cation for outstanding selective catalysis 査読有り

F. Kishimoto, T. Yoshioka, R. Ishibashi, H. Yamada, K. Muraoka, H. Taniguchi, T. Wakihara, K. Takanabe

Science advances 9 巻 ( 33 ) 2023年8月

Structural origins of the unusual thermal stability of amorphous CuxGe50-xTe50 (0 ≤ x ≤ 33.3) 査読有り国際共著

J.R. Stellhorn, B. Paulus, B.D. Klee, M. Inui, H. Taniguchi, Y. Sutou, S. Hosokawa, W.C. Pilgrim

Journal of Physics Condensed Matter 35 巻 ( 30 ) 2023年8月

Temperature-Stable Linear Dielectric Response of Low-Temperature Sintered La-Doped Bi2SiO5 Ceramics 査読有り

Y. Yasumoto, T. Kuwano, H. Taniguchi, S. Fujihara, M. Hagiwara

ACS Applied Electronic Materials 5 巻 ( 8 ) 頁： 4323 - 4329 2023年7月

Ferroelectricity in oxygen-deficient perovskite-type oxide Sr10Ga6Sc4O25 査読有り

A. Nakano, I. Terasaki, H. Taniguchi

Journal of Materials Chemistry C 11 巻 ( 25 ) 頁： 8541 - 8546 2023年6月

Ferroelectric Ionic Molecular Crystals with Significant Plasticity and a Low Melting Point: High Performance in Hot-Pressed Polycrystalline Plates and Melt-Grown Crystalline Sheets 査読有り

J. Harada, H. Takahashi, R. Notsuka, M. Takehisa, Y. Takahashi, T. Usui, H. Taniguchi

Angewandte Chemie - International Edition 62 巻 ( 3 ) 頁： e202215286 2023年1月

エマージェント物性を生みだす超秩序構造の創出ー特に誘電体材料に関してー査読有り

谷口博基

セラミックス 58 巻頁： 505 - 508 2023年

Controlling dielectric properties of Nb + X (X = Al, Ga, In) co-doped and Nb-doped rutile-type TiO2 single crystals 査読有り

S. Kakimoto, Y. Hashimoto, T. Kuwano, K. Kimura, K. Hayashi, M. Hagiwara, K. Deguchi, H. Taniguchi

Journal of Materials Chemistry C 11 巻 ( 4 ) 頁： 1304 - 1310 2022年12月

Hyper-Ordered Structures in Dielectric Materials 査読有り国際共著

M. Deluca, H. Taniguchi

Journal of the Physical Society of Japan 91 巻 ( 9 ) 頁： 091001 2022年9月

Phase variation of ferroelectric Li2Sr1−xCax(Nb1−xTax)2O7 by selective reinforcement in the (Nb,Ta)-O covalent bonds 査読有り

A. Nakano, H. Shirakuni, T. Nagai, Y. Mochizuki, F. Oba, H. Yokota, S. Kawaguchi, I. Terasaki, H. Taniguchi

Physical Review Materials 6 巻 ( 4 ) 頁： 044412 2022年4月

High-Pressure Thermopower of the Mott Insulator Ca2RuO4 査読有り

I. Sano, T. Nakano, A. Nakano, H. Taniguchi, F. Nakamura, I. Terasaki

Journal of the Physical Society of Japan 91 巻 ( 3 ) 頁： 033703 2022年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

We have measured and analyzed the thermopower of single-crystal samples of the Mott insulator Ca2RuO4 in high pressure up to 0.9 GPa. We find that the thermopower rapidly changes at a metal-insulator transition temperature, which is explained in terms of a percolation theory. In contrast, the thermopower in the insulator phase slightly decreases with increasing pressure well below the transition temperature, and is associated with thermodynamic quantities through the Kelvin formula. The pressure dependence is compared with the current-density dependence, and a possible origin for the current-enhanced thermopower is proposed.

DOI： 10.7566/JPSJ.91.033703

Size effect of the guest cation on the AlO4 framework in aluminate sodalite-type oxides M8[Al12O24](SO4)2 (M = Sr2+ and Ca2+) in the I43m phase 査読有り

A large piezoelectric voltage coefficient in aluminate-sodalite-type improper ferroelectric oxides 査読有り

H. Taniguchi, T. Hattori, T. Isobe, A. Nakano, I. Terasaki, M. Hagiwara

Journal of Materials Chemistry C 9 巻 ( 43 ) 頁： 15649 - 15653 2021年11月

Nontrivial Spin Dimer in the Hexagonal Ruthenate Ba3CaRu2O9 Revealed by Nonmagnetic Ion Substitution 査読有り

D. Nishihara, A. Kimura, A. Nakano, H. Taniguchi, I. Terasaki

Journal of the Physical Society of Japan 90 巻 ( 11 ) 頁： 114706 2021年11月

Giant Peltier conductivity in an uncompensated semimetal Ta2PdSe6 査読有り

A. Nakano, A. Yamakage, U. Maruoka, H. Taniguchi, Y. Yasui , I. Terasaki

3 巻 ( 4 ) 2021年10月

Thermal Diffusivity of the Mott Insulator Ca2RuO4 in a Non-equilibrium Steady State 査読有り

Shuji Kawasaki, Akitoshi Nakano, Hiroki Taniguchi, Hai Jun Cho, Hiromichi Ohta, Fumihiko Nakamura, Ichiro Terasaki

Journal of the Physical Society of Japan 90 巻 ( 6 ) 頁： 063601 - 063601 2021年6月

Thermal Diffusivity of the Mott Insulator Ca₂RuO₄ in a Non-equilibrium Steady State 査読有り

K. Shuji, N. Akitoshi, T. Hiroki, C. H. Jun, O. Hiromichi, N. Fumihiko, I. Terasaki

Journal of the Physical Society of Japan 90 巻 ( 6 ) 頁： 63601 - 1-5 2021年6月

Unconventional high-temperature ferromagnetic semiconductor PbPd1-x-yFeyLix O2 査読有り国際共著

Y. He, D. Sato, K. Misawa, D. Nishihara, A. Kimura, A. Nakano, H. Taniguchi, I. Terasaki

Journal of Applied Physics 129 巻 ( 20 ) 頁： 203903 2021年5月

Fabrication of bismuth silicate Bi2SiO5 ceramics as a potential high-temperature dielectric material 査読有り

K. Sakamoto, M. Hagiwara, H. Taniguchi, S. Fujihara

Journal of Materials Science 56 巻 ( 14 ) 頁： 8415 - 8426 2021年5月

Y. Nakahira, G. Kawamura, T. Wakamatsu, I. Terasaki, H. Taniguchi, Y. Kuroiwa, C. Moriyoshi

Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials 77 巻頁： 186 - 192 2021年4月

Room Temperature Thermoelectric Properties of Isostructural Selenides Ta2PdS6 and Ta2PdSe6 査読有り

A. Nakano, U. Maruoka, F. Kato, H. Taniguchi, I. Terasaki

Journal of the Physical Society of Japan 90 巻 ( 3 ) 頁： 33702 - 33702 2021年3月

Ga-substitution effects on the improper ferroelectric phase transition of Ca8[AlO2]12(MoO4)2 査読有り

K. Maruyama, A. Nakano, I. Terasaki, H. Taniguchi

Open Ceramics 5 巻 2021年3月

Coexisting Mechanisms for the Ferroelectric Phase Transition in Li2SrNb2O7 査読有り

Y. Mochizuki, T. Nagai, H. Shirakuni, A. Nakano, F. Oba, I. Terasaki, H. Taniguchi

Chemistry of Materials 33 巻 ( 4 ) 頁： 1257 - 1264 2021年2月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER CHEMICAL SOC

Pseudo-Ruddlesden-Popper-type Li2SrNb2O7 (LSNO), which belongs to a layered perovskite-type family, exhibits a first-order ferroelectric phase transition at 217 K. Our first-principles calculations and dielectric measurements show that Ca-substitution for Sr in LSNO enhances the rotation of NbO6 octahedra and Nb5+ displacements to induce a robustly stabilized ferroelectric P2(1)cn phase. The present study has demonstrated the two coexisting mechanisms in the ferroelectric phase transition of LSNO: the second-order Jahn-Teller effect and the rotational-distortion driven hybrid-improper ferroelectricity. The origin of unique ferroelectric phase transition of LSNO has been clarified to be softening of the zone-boundary Y-2(-) mode. The present study provides a new insight into designing ferroelectricity in layered perovskite-type oxides with the second-order Jahn-Teller effect and the rotations of octahedra.

DOI： 10.1021/acs.chemmater.0c04032

Nanoscale structural analysis of Pb(Mg1/3Nb2/3)O3 査読有り

Y. Yoneda, H. Taniguchi, Y. Noguchi

Journal of Physics: Condensed Matter 33 巻 ( 3 ) 頁： 035401 - 035401 2021年1月

Lamellar-like nanostructure in a relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3 査読有り

Y. Sato, S. Fujinaka, S. Yamaguchi, R. Teranishi, K. Kaneko, T. Shimizu, H. Taniguchi, H. Moriwake

Journal of Materials Science 56 巻 ( 2 ) 頁： 1231 - 1241 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）

The nanostructure of relaxor ferroelectric materials has been a central focus for investigating the microscopic origin of their intriguing physical properties. While it is believed that relaxor ferroelectricity is governed by polar nanostructures, such as polar nanoregions or nanodomains, recent studies have indicated the importance of additional mechanisms, such as the competition of ferroelectric/anti-ferroelectric order and the formation of hierarchical nanodomains. This calls for further investigation on the nanostructure. Here, we used conventional, in situ, and atomic-scale electron microscopy to study prototypic relaxor ferroelectrics, Pb(Mg Nb )O (PMN) and Pb(Mg Nb )O –PbTiO (PMN-PT). We found that a lamellar-like nanostructure was present in pure PMN, which had been overlooked in past studies and did not have a strong correlation with the polar nanostructure and the chemically ordered region. Unlike the lamellar-like nanodomains in PMN-PT, the lamellar-like nanostructure in PMN was not coupled with Pb-ion displacement and was not reoriented by the presence of an electric field. The results suggested that the formation of a lamellar-like structure occurs prior to the formation of larger-scale polar order in relaxor ferroelectrics. 1/3 2/3 3 1/3 2/3 3 3

DOI： 10.1007/s10853-020-05417-5

Firing Temperature of Ancient Ceramic Shards Estimated by Terahertz Spectroscopy

Niijima S., Taniguchi H., Kawase K.

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2020-November 巻頁： 341 - 342 2020年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

We propose a novel and accurate method of estimating the firing temperature of ancient ceramics using terahertz (THz) wave technology. The method is based on the firing temperature dependence of the THz-wave characteristics of ceramics. Using this method, the firing temperature of an ancient Arita porcelain shard was estimated at 1240 °C, which is within the firing temperature range estimated from other methods but is more precise.

DOI： 10.1109/IRMMW-THz46771.2020.9370497

Improper relaxor state in (Ca1-xSrx)8[Al O2]12(Mo O4)2

Nakamori H., Terasaki I., Taniguchi H.

Physical Review Materials 4 巻 ( 10 ) 2020年10月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review Materials

Dielectric and elastic properties of aluminate-sodalite-type oxides, (Ca1-xSrx)8[AlO2]12(MoO4)2 with x=1/16 and 1/4, are investigated in the present study. A well-defined improper ferroelectric phase transition is demonstrated in the composition of x=1/16 by the onset of spontaneous strain and sharp anomalies in the dielectric and elastic responses around 600 K. As the Sr concentration increases to x=1/4, strong frequency dispersion appears in the dielectric and elastic responses, indicating that the system changes into a short-range ordered state. The dielectric and elastic anomalies are found to follow a single Vogel-Fulcher equation over a wide frequency range from 10-1 to 106Hz. The present results suggest an improper relaxor state at the composition of x=1/4, in which polar nanoregions form under spatially heterogeneous strain due to differences in the local coordination environments around Ca and Sr.

DOI： 10.1103/PhysRevMaterials.4.104413

Permittivity boosting in "yellow" (Nb + In) co-doped TiO<inf>2</inf>

Taniguchi H., Sato D., Nakano A., Terasaki I.

Journal of Materials Chemistry C 8 巻 ( 39 ) 頁： 13627 - 13631 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Materials Chemistry C

Unusual effects of post annealing on optical and dielectric properties of (Nb0.5In0.5)0.01Ti0.99O2 (NITO-1.0%) are reported in the present study. The post-annealing performed under embedding in Al2O3 powder changes the color of a NITO-1.0% single crystal from black to yellow. Furthermore, the apparent increase in the relative permittivity due to the Maxwell-Wagner-Sillars effect, on the order of 104, observed in the as-synthesized NITO-1.0% completely disappears after the post-annealing to reveal an intrinsic enhancement of dielectric response due to the co-doping of Nb and In. The relative permittivity of the post-annealed NITO-1.0% uniformly increases by approximately 120 from the original value of pure-TiO2 over a wide temperature range from 4.2 K to room temperature. A temperature dependence of permittivity in the post-annealed NITO-1.0% shows behavior that is qualitatively identical to that of pure TiO2, indicating that the co-doping gives rise to an additional dielectric response in TiO2, probably through creation of defect complexes with large polarizability. The polarizability of the defect complex is estimated to be two hundred times greater than that of Ti4+, giving a new insight for the design of novel dielectric materials with large permittivity by means of complex defect engineering.

DOI： 10.1039/d0tc03539d

Ferroelectric and dielectric properties of improper ferroelectric Ca<inf>8-x</inf>Sr<inf>x</inf>[Al<inf>12</inf>O<inf>24</inf>] (MoO<inf>4</inf>)<inf>2</inf>multilayer capacitors

Hirose S., Usui T., Tanaka M., Katsuya Y., Taniguchi H.

Journal of Applied Physics 128 巻 ( 9 ) 2020年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Applied Physics

Improper ferroelectric Ca8-xSrx[Al12O24](MoO4)2 (x = 0-2) multilayer capacitors (MLCs) were fabricated to study their dielectric and ferroelectric properties for their potential practical applications and reversible switching of electric polarization by an electric field. The substitution of Sr for Ca caused a structural change from polar orthorhombic to non-polar cubic phases at 297 K and decreased the ferroelectric phase transition temperature (Tc). Spontaneous polarization up to ∼0.6 μC/cm2 was performed at 297 K in Ca7.5Sr0.5[Al12O24](MoO4)2 and Ca7Sr[Al12O24](MoO4)2 MLCs by poling with an electric field of 10 MV/m. Furthermore, ferroelectric hysteresis loops from the electric polarization switching were successfully demonstrated in Ca8[Al12O24](MoO4)2 MLCs above 469 K by the application of a high electric field over 50 MV/m, and remnant electric polarization of ∼0.59 μC/cm2 was obtained at 573 K. The results introduce a new avenue for possible applications and new functionalities of improper ferroelectrics with an MLC structure.

DOI： 10.1063/5.0016533

Non-equilibrium Steady State in the Mott Insulator Ca<inf>2</inf>RuO<inf>4</inf>

Terasaki I., Sano I., Toda K., Kawasaki S., Nakano A., Taniguchi H., Cho H.J., Ohta H., Nakamura F.

Journal of the Physical Society of Japan 89 巻 ( 9 ) 2020年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have measured and analyzed the nonlinear conduction of the Mott insulator Ca2RuO4 with square wave and square-pulse currents around room temperature with an infrared camera as a contactless thermometer. By combining the thermal diffusivity measurements, we have found that the temperature increase due to self heating is explained by the conduction of the Joule heat through the sample to the heat bath. We further find a time scale of the nonlinear conduction to be 20 ms, which is consistent with thermal relaxation time of the sample. We propose that a steady dissipation of external energy flow characterizes the non-equilibrium steady state of Ca2RuO4, rather than a steady current flow.

DOI： 10.7566/JPSJ.89.093707

Non-equilibrium Steady State in the Mott Insulator Ca₂RuO₄

Terasaki Ichiro, Sano Isuzu, Toda Kosuke, Kawasaki Shuji, Nakano Akitoshi, Taniguchi Hiroki, Cho Hai Jun, Ohta Hiromichi, Nakamura Fumihiko

Journal of the Physical Society of Japan 89 巻 ( 9 ) 頁： 93707 - 1-5 2020年9月

Optical enhancement of dielectric permittivity in reduced lanthanum aluminate 査読有り

Nagai T., Kuwabara A., Kumagai Y., Terasaki I., Taniguchi H.

Physical Review B 101 巻 ( 18 ) 2020年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

When light is absorbed in solids, electrical conductivity is usually enhanced through generation of photodoped conductive carriers, known as photoconduction. Here we show UV-light absorption restrains photoconduction, but markedly enhances dielectric permittivity in a ceramic sample of LaAlO3 with defects introduced deliberately by reduction synthesis. Using systematic dielectric measurements under photoirradiation combined with computational studies for defect formation energies, we explain this unconventional photoinduced phenomenon in terms of photoexcited dipoles: The photoexcited electrons are trapped in in-gap states introduced by oxygen vacancies whereas photoexcited holes are localized in a valence-band maximum. Thus the created electron-hole pair acts as an electric dipole to enhance the dielectric permittivity. This unprecedented photoelectric effect does not only provide an alternative functionality for dielectric materials, but also paves the way for next-generation photoelectronic devices.

DOI： 10.1103/PhysRevB.101.184114

Current-induced Giant Lattice Deformation in the Mott Insulator Ca2RuO4

Current-induced Giant Lattice Deformation in the Mott Insulator Ca2RuO4 査読有り

Okazaki Ryuji, Kobayashi Kensuke, Kumai Reiji, Nakao Hironori, Murakami Youichi, Nakamura Fumihiko, Taniguchi Hiroki, Terasaki Ichiro

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 89 巻 ( 4 ) 2020年4月

Okazaki Ryuji, Kobayashi Kensuke, Kumai Reiji, Nakao Hironori, Murakami Youichi, Nakamura Fumihiko, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan 89 巻 ( 4 ) 頁： 44710 - 44710 2020年4月

Examination of Nonlinear Conductivity on the Excitonic Insulator Candidate Ta2NiSe5

Nakano Akitoshi, Maruoka Urara, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan 89 巻 ( 4 ) 頁： 45001 - 45001 2020年4月

Examination of Nonlinear Conductivity on the Excitonic Insulator Candidate Ta2NiSe5 査読有り

Akitoshi Nakano, Urara Maruoka, Hiroki Taniguchi, Ichiro Terasaki

Journal of the Physical Society of Japan 89 巻 ( 4 ) 頁： 045001 2020年4月

Phase Transition from Weak Ferroelectricity to Incipient Ferroelectricity in Li<inf>2</inf>Sr(Nb<inf>1- x</inf>Ta<inf>x</inf>)<inf>2</inf>O<inf>7</inf> 査読有り

Nagai T., Mochizuki Y., Shirakuni H., Nakano A., Oba F., Terasaki I., Taniguchi H.

Chemistry of Materials 32 巻 ( 2 ) 頁： 744 - 750 2020年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry of Materials

Pseudo Ruddlesden-Popper-type Li2SrNb2O7 undergoes a phase transition between paraelectric and weak ferroelectric phases at Tc (=217 K), whereas Ta-counterpart Li2SrTa2O7 stays paraelectric though its room temperature structure is identical to that of Li2SrNb2O7. In the present study, the ferroelectric phase transition of Li2Sr(Nb1-xTax)2O7 is investigated as a function of Ta-concentration x. As the Ta-concentration x increases, Tc is found to decrease monotonously, leading to the disappearance of the ferroelectricity at x = 0.4. This phase-transition suppression with increasing x in Li2Sr(Nb1-xTax)2O7 is supported by first-principles calculations, showing that the soft mode in Li2SrNb2O7 or the increase of x in Li2Sr(Nb1-xTax)2O7 enhances their bonding states. In the composition of x = 0.4, dielectric permittivity gradually increases on cooling to become independent of temperature around 0 K, indicating an incipient ferroelectricity of the system. Empirical analyses suggest existence of a quantum paraelectric state in a composition range of 0.3 < x < 0.4. The present study provides a novel playground to investigate a quantum para/ferroelectricity in layered-perovskite-type compounds.

DOI： 10.1021/acs.chemmater.9b04022

谷口博基

電気学会誌 140 巻 ( 1 ) 頁： 28-31 - 31 2020年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人電気学会

1．はじめに私たちの身の回りでは，さまざまなエレクトロニクスデバイス素子が利用されている。例えば，抵抗器は電荷の流れを制限し，キャパシタは電荷を蓄積する。これらのデバイス素子の特性を何らかの外部刺激によってコントロールすることで，より高度なデバイス動作が得られる。抵抗器

DOI： 10.1541/ieejjournal.140.28

Exciton Transport in the Electron–Hole System Ta₂NiSe₅

Antiferroelectric to Antiferroelectric-Relaxor Phase Transition in Calcium Strontium Sulfoaluminate 査読有り

Wakamatsu T., Kawamura G., Abe T., Nakahira Y., Kawaguchi S., Moriyoshi C., Kuroiwa Y., Terasaki I., Taniguchi H.

Inorganic Chemistry 58 巻 ( 22 ) 頁： 15410 - 15416 2019年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Inorganic Chemistry

Structural phase transitions of calcium strontium sulfoaluminate series, (Ca1-xSrx)8[AlO2]12(SO4)2 ((CS)AS-x) with x = 0.80-1.00, are systematically investigated by powder X-ray diffraction, dielectric measurements, and pyroelectric measurements, to clarify a phase diagram of (CS)AS-x (x = 0.80-1.00). A pure strontium sulfoaluminate, (CS)AS-1.00, is found to undergo three phase transitions, which take place successively on cooling from a prototypical cubic phase with the symmetry of Im3 m. Though the room-temperature phase of (CS)AS-1.00 was previously reported to be of polar Pcc2, the pyroelectric measurements clarified a nonpolar character of the crystal symmetry. The dielectric measurements suggest a possibility of an antiferroelectric ground state of (CS)AS-x in the Sr-rich compositions. As x decreases, the ground state changes to a short-range-ordered state, implying a unique phase transition from the antiferroelectric state to the antiferroelectric-relaxor state. The present study provides an intriguing playground for designing new ferro/antiferroelectric materials.

DOI： 10.1021/acs.inorgchem.9b02495

Nakano Akitoshi, Nagai Takayuki, Katayama Naoyuki, Sawa Hiroshi, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan 88 巻 ( 11 ) 頁： 113706 - 1-4 2019年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：日本物理学会

We have measured the dielectric constant and thermopower of single crystal samples of the excitonic insulator candidate Ta2NiSe5. The dielectric constant below 50 K shows relaxor-like relaxation, implying the existence of randomly distributed electric dipoles. We have evaluated the concentration of the dipoles to be 10^19 cm^−3 at 30 K, which gives a rough estimate of the exciton concentration in this compound. A large thermopower of 600 µV/K at 100 K suddenly drops toward zero down to 50 K, and this zero thermopower evidences the neutral particles flow against the applied temperature gradient. We have semi-quantitatively explained the above two anomalies in terms of spontaneously generated excitons at low temperatures where thermally excited holes are quenched.ファイル公開：2020/11/15

Weak Ferroelectricity in n = 2 Pseudo Ruddlesden-Popper-Type Niobate Li<inf>2</inf>SrNb<inf>2</inf>O<inf>7</inf> 査読有り

Nagai T., Shirakuni H., Nakano A., Sawa H., Moriwake H., Terasaki I., Taniguchi H.

Chemistry of Materials 31 巻 ( 16 ) 頁： 6257 - 6261 2019年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry of Materials

Li2SrNb2O7 (LSNO) crystallizes in a structure closely related to n = 2 Ruddlesden-Popper-type compounds, which are generally formed by intergrowth of two-dimensional perovskite-type blocks and rocksalt-type layers. The present study demonstrates the coexistence of spontaneous polarization and an anti-ferroelectric-like nonlinear response in LSNO at 80 K, suggesting weak ferroelectricity below the phase transition temperature of 217 K. A combination of first-principles calculations and single-crystal X-ray diffractions clarifies a polar P21cn structure for the ground state of LSNO, where an in-plane antiferroelectric displacement and an out-of-plane polar shift simultaneously take place. The present study offers a new perspective to design ferroelectric and antiferroelectric materials with Ruddlesden-Popper-type compounds.

DOI： 10.1021/acs.chemmater.9b02373

自然経過観察例と比較した乳児臍ヘルニアのテープ固定療法の有用性

谷口直之, 甲斐裕樹, 松尾進, 松浦俊治, 田口智章

日本小児外科学会雑誌 55 巻 ( 5 ) 頁： 920 - 926 2019年8月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：特定非営利活動法人日本小児外科学会

【目的】九州小児外科研究会参加施設に臍ヘルニア治療に関する後方視的アンケート調査結果を行い，その結果に基づき臍ヘルニアのテープ固定療法の有用性を検討した．【方法】症例登録期間は2013年1月から2015年12月までとし，2016年6月末時点での治療結果を集計した．【結果】九州・沖縄・山口地区の24施設から回答を得た．臍ヘルニアの治癒判定はヘルニア門の閉鎖とする施設が最も多く，アンケート結果集計でもこの基準を採用した．テープ固定治療を受けた乳幼児は1,320例で，治癒と判定された症例が908例，非治癒と判定された症例は158例，皮膚障害による治療中止例が48例，転居などで中途脱落した症例が206例であった．自然経過観察症例は，テープ固定症例より大幅に少なく333例であった．治癒と判定されたのが146例，非治癒が111例，転居などで転帰不明が76例であった．治癒率はテープ固定群85.2％，自然経過群56.8％であり，テープ固定群の治癒率が有意に高かった（p＜0.05，χ2乗検定）．また治癒までの期間もテープ固定群では治癒症例の約80％の症例が治療開始から4か月以内に治癒していたのに対し，自然経過群では治癒までに1年以上かかっている症例が多かった．【結論】臍ヘルニアのテープ固定療法は早期に治癒が得られる利点はあるが，治癒率は従来言われてきた2歳で90％という自然治癒率を超えていなかった．今回のアンケート調査による臍ヘルニアの自然治癒率は従来言われてきたものよりも低く，臍ヘルニアの自然治癒率は前向き研究による再調査が必要と思われる．

DOI： 10.11164/jjsps.55.5_920

Interplay between quantum paraelectricity and thermoelectricity in the photo-Seebeck effect in a SrTiO<inf>3</inf> single crystal 査読有り

Shiraishi Y., Tanabe K., Taniguchi H., Okazaki R., Terasaki I.

Journal of Applied Physics 126 巻 ( 4 ) 2019年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Applied Physics

We report the electrical conductivity and the Seebeck coefficient of a SrTiO 3 single crystal under 405-nm laser illumination from 10 to 30 K. We find that the photoconductivity exponentially increases with decreasing temperature, suggesting a gradual metal-insulator transition. Assuming the carrier mobility reported in the preceding studies, we have evaluated the carrier concentration to be 8 × 10 9 cm - 3 at maximum, which corresponds to 10 - 7 ppm impurities in the case of chemical doping. Such ultralow doping is realized only when the energy of the incident light is slightly lower than the bandgap. In this situation, the incident light penetrates the whole sample with a small probability of electron-hole creation. We find that the observed photo-Seebeck coefficient seriously disagrees with the calculated values from the carrier concentration. In order to remedy this discrepancy, we have proposed a phenomenological model in which the quantum paraelectric behavior of SrTiO3 screens the thermoelectric voltage.

DOI： 10.1063/1.5106384

Plastic/Ferroelectric Crystals with Easily Switchable Polarization: Low-Voltage Operation, Unprecedentedly High Pyroelectric Performance, and Large Piezoelectric Effect in Polycrystalline Forms 査読有り

Harada J., Kawamura Y., Takahashi Y., Uemura Y., Hasegawa T., Taniguchi H., Maruyama K.

Journal of the American Chemical Society 141 巻 ( 23 ) 頁： 9349 - 9357 2019年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the American Chemical Society

Molecular ferroelectric crystals have attracted growing interest as potential alternatives to conventional lead-based ceramic ferroelectrics. We have recently discovered that a class of compounds known as plastic crystals can show multiaxial ferroelectricity, which allows ferroelectric performance even in polycrystalline forms. Here, we report new plastic/ferroelectric ionic molecular crystals that exhibit remarkably small coercive electric fields at room temperature. The easily switchable ferroelectric polarization enables low-voltage switching operations and high-frequency performance. Such ferroelectric crystals can be readily processed into bulk polycrystalline forms with desired shapes that are characterized by unprecedentedly high pyroelectric figures of merit and large piezoelectricity. These multifunctional molecular crystals represent highly attractive prospects for device elements with a diverse range of applications, which will significantly boost the development of molecular ferroelectric crystals.

DOI： 10.1021/jacs.9b03369

Structural Phase Transitions and Possibility of the Relaxor-like State in Improper Ferroelectric Strontium-Substituted Calcium Sulfoaluminates

Wakamatsu Toru, Kawamura Genta, Abe Tomohiro, Kawaguchi Shogo, Moriyoshi Chikako, Kuroiwa Yoshihiro, Itoh Mitsuru, Terasaki Ichiro, Taniguchi Hiroki

Journal of the Physical Society of Japan 88 巻 ( 3 ) 頁： 34718 - 34718 2019年3月

High-pressure compressibility and electronic properties of bismuth silicate Bi2SiO5 from synchrotron experiments and first-principles calculations 査読有り

Girard A., Stekiel M., Morgenroth W., Taniguchi H., Milman V., Bosak A., Winkler B.

Physical Review B 99 巻 ( 6 ) 2019年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

The high-pressure structural properties of bismuth oxide Bi2SiO5 have been investigated up to 29 GPa using in situ powder synchrotron x-ray diffraction (XRD) and up to 50 GPa with density functional theory (DFT) calculations. We found a compressibility anomaly at about 20 GPa that is observed both in our XRD and DFT results. The rotation of the corner-connected SiO4 tetrahedra produces a straightening of the silicate chains, yielding a lower compressibility above 20 GPa for the structure with straight chains. We analyzed the stereochemical activity of the Bi3+ lone electron pair, which is found to decrease with increasing pressure, but it can still be identified in the calculated electron density difference maps at 50 GPa.

DOI： 10.1103/PhysRevB.99.064116

Local structure analysis of PbTiO<inf>3</inf> in high-temperature cubic phase 査読有り

Yoneda Y., Taniguchi H., Kitanaka Y., Noguchi Y.

Ferroelectrics 538 巻 ( 1 ) 頁： 57 - 62 2019年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Ferroelectrics

High-energy X-ray diffraction study was performed on lead titanate (PbTiO3). Short-range order structure was revealed using atomic pair-distribution function (PDF) method. In the high-temperature cubic phase, there is a large deviation between local and average structure. Especially, Pb atoms deviated from the cubic lattice framework, but establish Pb-O-Pb random network.

DOI： 10.1080/00150193.2019.1569986

Exciton transport in the electron–hole system Ta<inf>2</inf>NiSe<inf>5</inf> 査読有り

Nakano A., Nagai T., Katayama N., Sawa H., Taniguchi H., Terasaki I.

Journal of the Physical Society of Japan 88 巻 ( 11 ) 頁： 113706 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have measured the dielectric constant and thermopower of single crystal samples of the excitonic insulator candidate Ta2NiSe5. The dielectric constant below 50 K shows relaxor-like relaxation, implying the existence of randomly distributed electric dipoles. We have evaluated the concentration of the dipoles to be 1019 cm−3 at 30 K, which gives a rough estimate of the exciton concentration in this compound. A large thermopower of 600 µV=K at 100 K suddenly drops toward zero down to 50 K, and this zero thermopower evidences the neutral particles flow against the applied temperature gradient. We have semi-quantitatively explained the above two anomalies in terms of spontaneously generated excitons at low temperatures where thermally excited holes are quenched.

DOI： 10.7566/JPSJ.88.113706

Structural Phase Transitions and Possibility of the Relaxor-like State in Improper Ferroelectric Strontium-Substituted Calcium Sulfoaluminates 査読有り

Wakamatsu T., Kawamura G., Abe T., Kawaguchi S., Moriyoshi C., Kuroiwa Y., Itoh M., Terasaki I., Taniguchi H.

Journal of the Physical Society of Japan 88 巻 ( 3 ) 頁： 034718 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

Structural phase transitions of strontium-substituted calcium sulfoaluminates, (Ca1−xSrx)8[AlO2]12(SO4)2 [(CS)AS-x], are systematically investigated by powder X-ray diffraction (PXRD) and dielectric measurements. In a pure calcium sulfoaluminate (CS)AS-0.0, an unreported phase transition and dielectric anomaly are found in the low-temperature region below the ferroelectric phase-transition temperature. The XRD pattern recorded as a function of Sr substitution and temperature clearly resolves Tc suppression with Sr content x from a structural change perspective. Although no macroscopic change in the crystal structure is observed for (CS)AS-0.4, the broad dielectric peak with frequency dispersion remains for this composition, indicating the fragmentation of polar ordering. Furthermore, (CS)AS-0.4 shows a specific heat anomaly along with the broad dielectric peak, suggesting a relaxor-like short-range ordered state of the system.

DOI： 10.7566/JPSJ.88.034718

Indium-Free Amorphous Ca-Al-O Thin Film as a Transparent Conducting Oxide 査読有り

Sim S.H., Kang K.T., Lee S., Lee M., Taniguchi H., Kim S., Roh S., Oh J.H., Lee S.A., Bae J.S., Jang J.H., Hwang J., Han S., Park T., Choi W.S.

Chemistry of Materials 31 巻 ( 19 ) 頁： 8019 - 8025 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry of Materials

Transparent conducting oxide (TCO) is a promising material system for transparent electrodes, which is one of the most essential elements in current electronic and energy devices. In particular, In-based TCOs such as Sn:In2O3 (ITO) and In-Ga-Zn-O (IGZO) have shown large optical band gap and high electrical conductivity, sufficient for the applications. However, In is an expensive element, which hampers its facile industrial application. Moreover, In-based TCOs show an abrupt decrease in conductivity when their thickness decreases below ∼100 nm, possibly due to inhomogeneity within the thin films. Here, we introduce an amorphous Ca-Al-O (CAO) thin film as a promising candidate for the In-free TCOs. The amorphous CAO thin film has very low resistivity (∼10-5 ω cm) at room temperature, as well as high transparency in the visible region of the light spectrum (>80%). The isotropic Ca s-orbital in the conduction band is found to be responsible for the superior performance of CAO as a TCO. Owing to the exceptional structural homogeneity of the CAO thin film, thickness-independent transport characteristics are observed, maintaining its TCO performance down to 10 nm of thickness.

DOI： 10.1021/acs.chemmater.9b02399

間接型強誘電性を示すゼオライト型化合物

谷口博基

応用物理 88 巻 ( 10 ) 頁： 668-672 - 672 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人応用物理学会

我々のグループでは最近，ゼオライトの一種であるアルミネートソーダライト型化合物において「間接型強誘電性」と呼ばれる風変わりな強誘電性を示す物質群を見いだした．アルミネートソーダライト型化合物は地球上に豊富に存在し，また主として環境親和性の高い元素によって構成されている．これまでの強誘電体材料開発はペロブスカイト型化合物を中心として進められており，キャパシタや周波数フィルタなど多くのデバイス素子として実用化に至っている．それに対して強誘電性アルミネートソーダライト型化合物は，焦電発電素子材料として鉛系ペロブスカイト型化合物も上回る特性を有し，非ペロブスカイト型強誘電体開発の新しい可能性を示している．本稿では，誘電特性や分極特性に着目しつつアルミネートソーダライト型化合物の間接型強誘電性を概説し，間接型強誘電性との関連から焦電発電素子材料としての性能を議論する．

DOI： 10.11470/oubutsu.88.10_668

Systematic tuning of the photo-dielectric effect in Ba(Al<inf>1-</inf><inf>x</inf>Zn<inf>x</inf>)<inf>2</inf>O<inf>4-δ</inf> 査読有り

Ruddlesden-Popper型酸化物Li2SrNb2O7における誘電特性

永井隆之, 中埜彰俊, 森分博紀, 澤博, 寺崎一郎, 谷口博基

日本物理学会講演概要集 74.1 巻 ( 0 ) 頁： 2549 - 2549 2019年

放射光X線回折によるRuddlesden-Popper型酸化物Li2SrNb2O7の結晶構造解析

中埜彰俊, 永井隆之, 澤博, 寺崎一郎, 谷口博基

日本物理学会講演概要集 74.1 巻 ( 0 ) 頁： 2550 - 2550 2019年

アルミネートソーダライト型酸化物(Ca1-xSrx)8[AlO2]12(MoO4)2 (0.5≦x≦1.0) のリエントラント構造相転移

青木伸雅, 中埜彰俊, 中平夕貴, 森吉千佳子, 黒岩芳弘, 寺崎一郎, 谷口博基

日本物理学会講演概要集 74.1 巻 ( 0 ) 頁： 2551 - 2551 2019年

Nagai T., Tanabe K., Terasaki I., Taniguchi H.

Applied Physics Letters 113 巻 ( 21 ) 頁： 212902 2018年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Systematic tuning of photo-induced enhancement of the dielectric permittivity (i.e., the photo-dielectric effect) in Ba(Al1-xZnx)2O4-δ (BAZ-x) has been demonstrated by changing Zn concentration x and intensity of the incident light. The relative change of the dielectric permittivity (ϵ′), defined as Δϵ′photo/ϵ′dark, increases linearly with an increase in the Zn concentration (x), finally reaching approximately 30% at 1 MHz. The dependence of Δϵ′photo/ϵ′dark on the intensity of the incident light shows a two-step growth as the irradiation light intensity increases, suggesting the existence of multiple photo-induced processes influencing the photo-dielectric effect of BAZ-x. The results of the present study not only give a clue to the mechanism of the photo-dielectric effect but also aid in the development of innovative photo-tunable functional devices.

DOI： 10.1063/1.5036982

Spectroscopic signature of trimer Mott insulator and charge disproportionation in BaIrO3 査読有り

Okazaki R., Ito S., Tanabe K., Taniguchi H., Ikemoto Y., Moriwaki T., Terasaki I.

Physical Review B 98 巻 ( 20 ) 2018年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

We have measured the reflectivity spectra of the barium iridate 9RBaIrO3, the crystal structure of which consists of characteristic Ir3O12 trimers. In the high-temperature phase above the transition temperature Tc≃180 K, we find that the optical conductivity involves two temperature-dependent optical transitions with an ill-defined Drude response. These features are reminiscent of the optical spectra in the organic dimer Mott insulators, implying a possible emergence of an unusual electronic state named trimer Mott insulator in BaIrO3, where the carrier is localized on the trimer owing to the strong Coulomb repulsion. Along with a pronounced splitting of the phonon peak observed below Tc, which is a hallmark of charge disproportionation, we discuss a possible phase transition from the trimer Mott insulator to a charge-ordered insulating phase in BaIrO3.

DOI： 10.1103/PhysRevB.98.205131

Impurity-Induced Spin-State Crossover in La0.8Sr0.2Co1−xAlxO3 査読有り

Ichiro Terasaki, Masamichi Ikuta, Takafumi Yamamoto, Hiroki Taniguchi

Crystals 8 巻 ( 11 ) 頁： 411 2018年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：MDPI} {AG

We have prepared a set of polycrystalline samples of La0.8Sr0.2Co1−xAlxO3 (0 ≤ x ≤ 0.2), and have measured the magnetization as functions of temperature and magnetic field. We find that the average spin number per Co ion (SCo) evaluated from the room-temperature susceptibility is around 1.2–1.3 and independent of x. However, we further find that SCo evaluated from the saturation magnetization at 2 K is around 0.3–0.7, and decreases dramatically with x. This naturally indicates that a significant fraction of the Co3+ ions experience a spin-state crossover from the intermediate-to low-spin state with decreasing temperature in the Al-substituted samples. This spin-state crossover also explains the resistivity and the thermopower consistently. In particular, we find that the thermopower is anomalously enhanced by the Al substitution, which can be consistently explained in terms of an extended Heikes formula.

DOI： 10.3390/cryst8110411

Transport and Magnetic Properties of CaPd3−xCuxO4 (x ≤ 2.4) with Interconnecting Cu(Pd)O4 Chain Structure

Terasaki Ichiro, Misawa Kazuki, Tanabe Kenji, Taniguchi Hiroki

Journal of the Physical Society of Japan 87 巻 ( 10 ) 頁： 104603 - 104603 2018年10月

Competing structural instabilities in Bi2SiO5 査読有り

Girard A., Taniguchi H., Souliou S.M., Stekiel M., Morgenroth W., Minelli A., Kuwabara A., Bosak A., Winkler B.

Physical Review B 98 巻 ( 13 ) 2018年10月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

The lattice dynamics of Bi2SiO5 has been studied by x-ray thermal diffuse scattering (TDS), inelastic x-ray scattering (IXS), and density functional theory calculations across the ferroelectric transition at TC=663 K. Rodlike diffuse features are observed along the [100] direction, perpendicular to the direction of the quasi-one-dimensional silicate chains. IXS measurements of the phonon dispersion along the [100] Γ-Y direction related these diffuse features to coupled unstable transverse optic and acoustic branches. A strong temperature-dependent TDS signal was also observed at the Brillouin zone edges, at the Y and S points, indicating a competition between ferroelectric and antiferroelectric distortions. We observed with IXS a substantial but finite phonon softening at the Y point and a minor softening at the S point, that are associated with the displacement of oxygen atoms. The good agreement between the experiment and the theoretical TDS and IXS allows us to provide a quantitative overview of the various lattice dynamical instabilities occurring at TC. The direct evidence for competing ferroelectric and antiferroelectric orders opens the way towards tuning the properties of Bi2SiO5 by application of pressure or electrical field.

DOI： 10.1103/PhysRevB.98.134102

Dynamical coupling of dilute magnetic impurities with quantum spin liquid state in the S=3/2 dimer compound Ba3ZnRu2O9

Yamamoto Takafumi D., Taniguchi Hiroki, Terasaki Ichiro

JOURNAL OF PHYSICS-CONDENSED MATTER 30 巻 ( 35 ) 2018年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physics Condensed Matter

We have investigated the dilute magnetic impurity effect on the magnetic properties of a quantum spin liquid candidate Ba3ZnRu2O9 and a spin gapped compound Ba3CaRu2O9. The magnetic ground state of each compound stands against 2% substitution of magnetic impurities for Zn or Ca. We have found that the magnetic response of these impurities, which behave as paramagnetic spins, depends on the host materials and the difference of the two manifests itself in the Weiss temperature, which can hardly be explained by the dilute magnetic impurities alone in the case of Ba3ZnRu2O9. We consider a contribution from the Ru5+ ions which would appear only in the substituted Ba3ZnRu2O9 and discuss a possible physical meaning of the observed Weiss temperature.

DOI： 10.1088/1361-648X/aad5ac

Structural variations and dielectric properties of (B i1-x L ax)2Si O5 (0≤x≤0.1): Polycrystallines synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses STRUCTURAL VARIATIONS and DIELECTRIC ⋯ HIROKI TANIGUCHI et al. 査読有り

Taniguchi H., Tatewaki S., Yasui S., Fujii Y., Yamaura J., Terasaki I.

Physical Review Materials 2 巻 ( 4 ) 2018年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review Materials

This paper focuses on effects of isovalent La substitution on the crystal structure and dielectric properties of ferroelectric Bi2SiO5. Polycrystalline samples of (Bi1-xLax)2SiO5 are synthesized by crystallization of Bi-Si-O and Bi-La-Si-O glasses with a composition range of 0≤x≤0.1. The crystal structure changes from monoclinic to tetragonal with increasing La-substitution rate x at room temperature. This structural variation stems from the change in orientation of SiO4 tetrahedra that form one-dimensional chains when they are in the ordered configuration, thus suggesting that lone-pair electrons play an important role in sustaining one-dimensional chains of SiO4 tetrahedra. Synchronizing with the disordering of SiO4 chains, ferroelectric phase transition temperature of (Bi1-xLax)2SiO5 sharply decreases as x increases, and ferroelectricity finally vanishes at around x=0.03. The present results demonstrate that lone-pair electrons of Bi play an important role in the ferroelectricity of Bi2SiO5 through propping the ordered structure of one-dimensional SiO4 chains with stereochemical activity. Furthermore, an additional phase transition has been first discovered in the low-temperature region of (Bi1-xLax)2SiO5 with x≤0.01, where the ordered one-dimensional SiO4 chains remain.

DOI： 10.1103/PhysRevMaterials.2.045603

La0.8Sr0.2Co1-xAlxO3におけるスピン状態制御

Transport and magnetic properties of CaPd3-xCuxO4 (x ≤ 2.4) with interconnecting Cu(Pd)O4 chain structure 査読有り

Terasaki I., Misawa K., Tanabe K., Taniguchi H.

Journal of the Physical Society of Japan 87 巻 ( 10 ) 頁： 104603 2018年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have successfully synthesized a set of polycrystalline samples of CaPd3-xCuxO4 from x = 0 to 2.4, and measured the resistivity, thermopower and susceptibility down to 4K. We find that the solid solution between Pd and Cu systematically evolves the electronic ground states from a conventional band insulator to a correlated Mott insulator. In particular, CaPd0.6Cu2.4O4 shows a magnetic phase transition at 20 K. A partial substitution of La and Y for Ca supplies electrons to CaPd0.6Cu2.4O4, and decreases the room-temperature resistivity smaller than 10ωcm.

DOI： 10.7566/JPSJ.87.104603

永井隆之, 寺崎一郎, 谷口博基

日本物理学会講演概要集 73.2 巻 ( 0 ) 頁： 897 - 897 2018年

生田将理, 山本貴史, 田辺賢士, 谷口博基, 寺崎一郎

日本物理学会講演概要集 73.1 巻 ( 0 ) 頁： 2199 - 2199 2018年

間接型強誘電体(Ca1-xSrx)8[AlO2]12(MoO4)2の構造相転移と弾性応答

中森大貴, 寺崎一郎, 谷口博基

日本物理学会講演概要集 73.2 巻 ( 0 ) 頁： 2130 - 2130 2018年

Photo-induced persistent enhancement of dielectric permittivity in Zn:BaAl<inf>2</inf>O<inf>4</inf> 査読有り

Nagai T., Yamada Y., Tanabe K., Terasaki I., Taniguchi H.

Applied Physics Letters 111 巻 ( 23 ) 頁： 232902 2017年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Photo-induced persistent enhancement of dielectric permittivity has been demonstrated in Ba(Al0.97Zn0.03)2O4-δ (BAZ) with a stuffed-Tridymite-Type structure under photo-irradiation with an energy of 3.4 eV (365 nm). The dielectric permittivity is enhanced by more than 20% and shows a weak frequency dependency. The dielectric loss (tanδ) shows only a slight increment for frequencies up to 1 MHz, indicating that the incremental change in dielectric permittivity of BAZ is not caused by photoconduction. This enhancement persists on termination of photo-irradiation. The results of this study suggest that the origin of the enhancement of dielectric permittivity is related to the dielectric response of the photo-excited dipole moments, which are composed of photo-excited electrons trapped in in-gap states and photo-excited holes generated in the valence band maximum. These findings shed light on the development of devices that can control dielectric properties by photo-irradiation.

DOI： 10.1063/1.5001369

Intrinsic Enhancement of Dielectric Permittivity in (Nb + In) co-doped TiO<inf>2</inf> single crystals 査読有り

Kawarasaki M., Tanabe K., Terasaki I., Fujii Y., Taniguchi H.

Scientific Reports 7 巻 ( 1 ) 頁： 5351 2017年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scientific Reports

The development of dielectric materials with colossal permittivity is important for the miniaturization of electronic devices and fabrication of high-density energy-storage devices. The electron-pinned defect-dipoles has been recently proposed to boost the permittivity of (Nb + In) co-doped TiO2 to 105. However, the follow-up studies suggest an extrinsic contribution to the colossal permittivity from thermally excited carriers. Herein, we demonstrate a marked enhancement in the permittivity of (Nb + In) co-doped TiO2 single crystals at sufficiently low temperatures such that the thermally excited carriers are frozen out and exert no influence on the dielectric response. The results indicate that the permittivity attains quadruple of that for pure TiO2. This finding suggests that the electron-pinned defect-dipoles add an extra dielectric response to that of the TiO2 host matrix. The results offer a novel approach for the development of functional dielectric materials with large permittivity by engineering complex defects into bulk materials.

DOI： 10.1038/s41598-017-05651-z

Magneto-thermopower in the weak ferromagnetic oxide CaRu<inf>0.8</inf>Sc<inf>0.2</inf>O<inf>3</inf>: An experimental test for the Kelvin formula in a magnetic material 査読有り

Yamamoto T., Taniguchi H., Yasui Y., Iguchi S., Sasaki T., Terasaki I.

Journal of the Physical Society of Japan 86 巻 ( 10 ) 頁： 104707 2017年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have measured the resistivity, the thermopower, and the specific heat of the weak ferromagnetic oxide CaRu0.8Sc0.2O3 in external magnetic fields up to 140 kOe below 80 K. We have observed that the thermopower Q is significantly suppressed by magnetic fields at around the ferromagnetic transition temperature of 30 K, and have further found that the magneto-thermopower QðH; TÞ ¼ QðH; TÞ Qð0; TÞ is roughly proportional to the magneto-entropy SðH; TÞ ¼ SðH; TÞ Sð0; TÞ. We discuss this relationship between the two quantities in terms of the Kelvin formula, and find that the observed ΔQ is quantitatively consistent with the values expected from the Kelvin formula, a possible physical meaning of which is discussed.

DOI： 10.7566/JPSJ.86.104707

Magneto-thermopower in the Weak Ferromagnetic Oxide CaRu0.8Sc0.2O3: An Experimental Test for the Kelvin Formula in a Magnetic Material

Yamamoto Takafumi D., Taniguchi Hiroki, Yasui Yukio, Iguchi Satoshi, Sasaki Takahiko, Terasaki Ichiro

Journal of the Physical Society of Japan 86 巻 ( 10 ) 頁： 104707 - 104707 2017年10月

Enhancement of the dielectric permittivity of (Nb<inf>1/2</inf>In<inf>1/2</inf>)<inf>0.02</inf>Ti<inf>0.98</inf>O<inf>2</inf> single crystals at low temperatures due to (Nb + In) codoping 査読有り

Taniguchi H., Ando K., Terasaki I.

Japanese Journal of Applied Physics 56 巻 ( 10 ) 2017年10月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Japanese Journal of Applied Physics

Dielectric measurements are performed on (Nb1/2In1/2)0.02Ti0.98O2 (NITO-2.0) single crystals grown by a floating zone method to address the nature of the colossal permittivity recently reported in (Nb + In) co-doped TiO2 ceramics. The colossal permittivity of the order of 105, which is also observed in the NITO-2.0 single crystals, disappears in the lowest temperature region, indicating an extrinsic contribution from thermally excited carriers to the colossal permittivity. Even at low temperatures where the thermally excited carriers are expected to be frozen out, a high permittivity of the order of 103 remains. This finding suggests that an intrinsic contribution from electron-pinned defect dipoles boosts the dielectric permittivity of TiO2.

DOI： 10.7567/JJAP.56.10PC02

Magnetoelectric coupling in the pyrochlore ruthenate Gd<inf>2</inf>Ru<inf>2</inf>O<inf>7</inf> 査読有り

Okamura T., Okazaki R., Taniguchi H., Yasui Y., Terasaki I.

Journal of the Physical Society of Japan 86 巻 ( 8 ) 頁： 084708 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have prepared polycrystalline samples of Gd2Ru2O7, and have measured the dielectric constant, magnetization and magnetostriction in external fields from 0 to 7 T below 15 K. We find that the dielectric constant of Gd2Ru2O7 significantly changes with external fields, and reveal a finite magnetoelectric coupling in this oxide. Using a simple model in which the spins on the Gd ions feel an internal magnetic field of 7 T from the Ru clusters, we have explained magnetization and magnetoelectric effects qualitatively.

DOI： 10.7566/JPSJ.86.084708

Magnetoelectric Coupling in the Pyrochlore Ruthenate Gd2Ru2O7

Okamura Takuma, Okazaki Ryuji, Taniguchi Hiroki, Yasui Yukio, Terasaki Ichiro

Journal of the Physical Society of Japan 86 巻 ( 8 ) 頁： 84708 - 84708 2017年8月

Giant inductance in non-ohmic conductor 査読有り

Tanabe K., Taniguchi H., Nakamura F., Terasaki I.

Applied Physics Express 10 巻 ( 8 ) 2017年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

An inductor is composed of a coil, and its design has seen little progress since its inception more than one hundred years ago. We propose a novel method of inducing inductance in a non-ohmic conductor. In this paper, we report a giant inductance of 42H in Ca2RuO4 in the low frequency region at room temperature, as an example. The quality (Q) factor, defined as the ratio between the imaginary and real parts of impedance, approaches infinity in the static limit. Our inductor, therefore, displays ideal characteristics such as a large inductance and high Q factor, and it may be a prime candidate for next-generation inductors.

DOI： 10.7567/APEX.10.081801

リラクサーPb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$の局所構造解析査読有り

米田安宏, 谷口博基, Fu, D

Ferroelectrics 513 巻 ( 1 ) 頁： 1 - 6 2017年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ferroelectrics

リラクサー強誘電体Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$の局所構造解析をExtended X-ray Absorption Fine Structure (EXAFS)を用いて行った。Nb周辺の局所構造をAgNbO$_3$と比較し、Pb周辺の局所構造をPbTiO$_3$と比較した。PMNのNb周辺構造はAgNbO$_3$とよく一致しており、AgNbO$_3$と同様のNb off-center shiftに起因する1.91と2.01{\AA}の2つの結合に分裂していた。一方、disorderしたPbサイトはPDF解析から構造を抽出することに成功した。

DOI： 10.1080/00150193.2017.1350050

Broadband micro light scattering observation of ferroelectric sodium metavanadate 査読有り

Fujii Y., Katayama D., Morita M., Koreeda A., Taniguchi H., Terasaki I.

Ferroelectrics 512 巻 ( 1 ) 頁： 14 - 19 2017年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ferroelectrics

Sodium metavanadate has pyroxene-type one dimensional VO4-tetrahedral chains, which is analogous to the SiO4-chains in Bi2SiO5. Although it is known to undergo ferroelectric phase transition, its mechanism has not been clarified. This paper shows the spectroscopic results of simultaneous measurement of Raman/Brillouin scattering by utilizing ultra-narrowband holographic notch filters. The spectroscopic anomalies accompanying to the phase transition were observed for the first time in both Raman and Brillouin regimes.

DOI： 10.1080/00150193.2017.1355146

Optical evidence for the spin-state disorder in LaCo<inf>1-x</inf>Rh<inf>x</inf>O<inf>3</inf> 査読有り

Terasaki I., Asai S., Taniguchi H., Okazaki R., Yasui Y., Ikemoto Y., Moriwaki T.

Journal of Physics Condensed Matter 29 巻 ( 23 ) 頁： 235802 2017年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physics Condensed Matter

We have measured the infrared reflectivity of single-crystalline samples of LaCo1-xRhxO3 (x = 0, 0.05 and 0.10) from 10 to 300 K from 0.05 to 0.15 eV. We find that the optical phonons of the Co-O stretching mode depend on temperature and the Rh content. Analysis with three Lorentz oscillators reveals that the spin state of Co3+ in LaCo1-xRhxO3 can be understood in terms of a solid solution of low-spin- and high-spin-state Co3+ ions, and the substituted Rh ion retains some fraction of the high-spin Co3+ ions down to low temperature.

DOI： 10.1088/1361-648X/aa6ebc

Oxide heterostructure research in Korea 査読有り

Choi W.S., Park S., Taniguchi H., Noh T.W.

Current Applied Physics 17 巻 ( 5 ) 頁： 593 - 594 2017年5月

COPD Assessment Test for measurement of health status in patients with idiopathic pulmonary fibrosis: A cross-sectional study

Matsuda Toshiaki, Taniguchi Hiroyuki, Ando Masahiko, Kondoh Yasuhiro, Kimura Tomoki, Kataoka Kensuke, Sakamoto Koji, Suzuki Atsushi, Furukawa Taiki, Hasegawa Yoshinori

RESPIROLOGY 22 巻 ( 4 ) 頁： 721-727 2017年5月

Improper ferroelectrics as high-efficiency energy conversion materials 査読有り

Wakamatsu T., Tanabe K., Terasaki I., Taniguchi H.

Physica Status Solidi - Rapid Research Letters 11 巻 ( 5 ) 頁： 1700009 2017年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physica Status Solidi - Rapid Research Letters

An improper ferroelectric is a certain type of ferroelectrics whose primary order parameter is not polarization but another physical quantity such as magnetization. In contrast to a conventional proper ferroelectrics as represented by Pb(Zr,Ti)O3 and BaTiO3, the improper ferroelectrics has been inconceivable for practical applications thus far. Herein, we illustrate the great potential of improper ferroelectrics for efficient conversion of temperature fluctuation to electric energy, as demonstrated with (Ca0.84Sr0.16)8[AlO2]12(MoO4)2 (CSAM-16). The present study has experimentally proven that CSAM-16 achieves an excellent electrothermal coupling factor and high electric field sensitivity for pyroelectric energy conversion that approach a practical level for application to self-powered autonomous electronic devices for rapidly spreading wireless sensor networks. The present results provide a novel approach to developing innovative pyroelectric energy harvesting devices using improper ferroelectrics.

DOI： 10.1002/pssr.201700009

Optical control of dielectric permittivity in LaAl<inf>0.99</inf>Zn<inf>0.01</inf>O<inf>3-δ</inf> 査読有り

Nagai T., Takahashi H., Okazaki R., Tanabe K., Terasaki I., Taniguchi H.

Applied Physics Letters 110 巻 ( 17 ) 2017年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

A photo-dielectric effect (i.e., a change in dielectric permittivity due to photo-irradiation) has been demonstrated in LaAl0.99Zn0.01O3-δ. Photo-irradiation with an incident energy of 3.4 eV was found to enhance the dielectric permittivity in LaAl0.99Zn0.01O3-δ over a wide frequency range from 100 Hz to 1 MHz. The change in dielectric permittivity in the high-frequency region hardly depended on frequency and was not accompanied by an increase in dielectric loss, indicating an intrinsic photo-dielectric effect in LaAl0.99Zn0.01O3-δ that is not due to photo-conduction. The dependence of the photo-dielectric effect on incident energy suggests the existence of deep in-gap states introduced by Zn substitution. The mechanism of the photo-dielectric effect in LaAl0.99Zn0.01O3-δ relates to the dielectric response of the photo-excited electrons trapped in the deep in-gap states, which work as effective polar displacements under an applied electric field. These findings are expected to contribute to the development of photo-capacitors that enable the remote control of the dielectric response via photo-irradiation.

DOI： 10.1063/1.4979644

Improper Ferroelectricity in Stuffed Aluminate Sodalites for Pyroelectric Energy Harvesting 査読有り

Maeda Y., Wakamatsu T., Konishi A., Moriwake H., Moriyoshi C., Kuroiwa Y., Tanabe K., Terasaki I., Taniguchi H.

Physical Review Applied 7 巻 ( 3 ) 2017年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review Applied

In the present study, we demonstrate ferroelectricity in stuffed aluminate sodalites (Ca1-xSrx)8[AlO2]12(WO4)2 (x≤0.2) (C1-xSxAW). Pyroelectric measurements clarify switchable spontaneous polarization in polycrystalline C1-xSxAW, whose polarization values are on the order of 10-2 μC/cm2 at room temperature. A weak anomaly in the dielectric permittivity at temperatures near the ferroelectric transition temperature suggests improper ferroelectricity of C1-xSxAW for all investigated values of x. A comprehensive study involving synchrotron x-ray powder diffraction measurements, molecular dynamics simulations, and first-principles calculations clarifies that the ferroelectric phase transition of C1-xSxAW is driven by the freezing of the fluctuations of WO4 tetrahedra in the voids of an [AlO2]1212- framework. The voltage response and electromechanical coupling factor of C1-xSxAW estimated from the present results indicate that this material exhibits excellent performance as a pyroelectric energy harvester, suggesting that aluminate sodalites exhibit great promise as a class of materials for highly efficient energy-harvesting devices.

DOI： 10.1103/PhysRevApplied.7.034012

Absence of Magnetic Long Range Order in Ba3ZnRu2O9: A Spin-Liquid Candidate in the S = 3/2 Dimer Lattice

Terasaki Ichiro, Igarashi Taichi, Nagai Takayuki, Tanabe Kenji, Taniguchi Hiroki, Matsushita Taku, Wada Nobuo, Takata Atsushi, Kida Takanori, Hagiwara Masayuki, Kobayashi Kensuke, Sagayama Hajime, Kumai Reiji, Nakao Hironori, Murakami Youichi

Journal of the Physical Society of Japan 86 巻 ( 3 ) 頁： 33702 - 33702 2017年3月

Absence of magnetic long range order in Ba<inf>3</inf>ZnRu<inf>2</inf>O<inf>9</inf>: A spin-liquid candidate in the S = 3/2 dimer lattice 033702 査読有り

Terasaki I., Igarashi T., Nagai T., Tanabe K., Taniguchi H., Matsushita T., Wada N., Takata A., Kida T., Hagiwara M., Kobayashi K., Sagayama H., Kumai R., Nakao H., Murakami Y.

Journal of the Physical Society of Japan 86 巻 ( 3 ) 頁： 033702 2017年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have discovered a novel candidate for a spin liquid state in a ruthenium oxide composed of dimers of S = 3/2 spins of Ru5+, Ba3ZnRu2O9. This compound lacks a long range order down to 37 mK, which is a temperature 5000-times lower than the magnetic interaction scale of around 200 K. Partial substitution for Zn can continuously vary the magnetic ground state from an antiferromagnetic order to a spin-gapped state through the liquid state. This indicates that the spin-liquid state emerges from a delicate balance of inter- and intra-dimer interactions, and the spin state of the dimer plays a vital role. This unique feature should realize a new type of quantum magnetism.

DOI： 10.7566/JPSJ.86.033702

強誘電性シリケートBi2SiO5のLa置換効果

帯刀信吾, 酒井雄樹, 藤井康裕, 是枝聡肇, 安井伸太郎, 東正樹, 田辺賢士, 寺崎一郎, 谷口博基

日本物理学会講演概要集 72.1 巻 ( 0 ) 頁： 2719 - 2719 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

Bi_2_SiO_5_は室温以上で強誘電性を示すシリケート化合物である。本研究ではBi_2_SiO_5_中のBiをLaで1%〜10%置換した試料を作製し、誘電率測定を行った。その結果、La置換による相転移のブロード化が観測され、置換率3％で相転移が消失した。相転移が消失した試料では100〜500 Kにわたって温度変化がほとんどない、高誘電率(ε’ 〜 100)が得られた。講演では、誘電応答の起源を格子ダイナミクスの観点から議論する予定である。

DOI： 10.11316/jpsgaiyo.72.1.0_2719

磁場中熱伝導率測定で探るCaRu1-xScxO3の不純物誘起強磁性

山本貴史, 谷口博基, 寺崎一郎

日本物理学会講演概要集 72.2 巻 ( 0 ) 頁： 2057 - 2057 2017年

Colossal Seebeck effect enhanced by quasi-ballistic phonons dragging massive electrons in FeSb 2 査読有り

Takahashi H., Okazaki R., Ishiwata S., Taniguchi H., Okutani A., Hagiwara M., Terasaki I.

Nature Communications 7 巻 2016年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Nature Communications

Phonon transport is an essential property of thermoelectric materials. Although the phonon carries heat, which reduces the thermoelectric efficiency, it contributes positively to the Seebeck coefficient S through the phonon-drag effect, as typified by the high-purity semiconductors, which show fairly large S at cryogenic temperatures. Although such a large S is attractive in terms of Peltier cooling, a clear guiding principle for designing thermoelectric materials enriched by the phonon-drag effect remains to be established. Here we demonstrate that a correlated semiconductor, FeSb2, is a promising thermoelectric material featuring quasi-ballistic phonons dragging d electrons with large effective mass. By changing the sample size within the sub-millimetre order for high-purity single crystals, we succeed in substantially increasing S to as much as -27 mV K-1 at low temperatures. Our results exemplify a strategy for exploring phonon-drag-based thermoelectric materials, the performance of which can be maximized by combining heavy electrons with ballistic phonons.

DOI： 10.1038/ncomms12732

Optical sheet conductivities of layered oxides 査読有り

Tanabe K., Taniguchi H., Terasaki I.

Journal of Physics Condensed Matter 28 巻 ( 32 ) 頁： 325501 2016年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physics Condensed Matter

We report on the optical properties of the layered Co oxides Bi2-xPbxSr2Co2O8 with x = 0 and 0.4 and discuss similarities among optical sheet conductivities of layered Co and Cu oxides. Optical sheet conductivity is defined as the product of the optical conductivity and the lattice parameter along the cross-layer direction. Although the optical conductivity spectra of both Bi2-xPbxSr2Co2O8 with x = 0 and 0.4 are similar in shape to Na0.75CoO2 and Ca3Co4O9 below 3 eV, they are much smaller in magnitude. In contrast, optical sheet conductivities are roughly identical among the four Co oxides below 3 eV, which indicates that the common CoO2 layer in these oxides has the same electronic state. In addition, we find that optical sheet conductivities are identical among the layered Cu oxides with a four-fold coordinated CuO4 plane. We suggest using optical sheet conductivity as a key concept to discuss the similarity among the layered materials.

DOI： 10.1088/0953-8984/28/32/325501

Two competing soft modes and an unusual phase transition in the stuffed tridymite-type oxide BaAl2 O4 査読有り

Ishii Y., Mori S., Nakahira Y., Moriyoshi C., Park J., Kim B.G., Moriwake H., Taniguchi H., Kuroiwa Y.

Physical Review B 93 巻 ( 13 ) 2016年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B

We investigated the structural phase transition of BaAl2O4, which has a network structure with corner-sharing AlO4 tetrahedra, via synchrotron x-ray thermal diffuse scattering measurements and first-principles calculations. BaAl2O4 shows the structural phase transition at TC=451.4 K from the P6322 parent crystal structure to the low-temperature superstructure with a cell volume of 2a×2b×c. This phase transition is unusual, in which two energetically competing phonon modes at M and K points soften simultaneously. When approaching TC from above, the K-point mode appears first. However, this K-point mode is overcome by the later-developed M-point mode. The thermal diffuse scattering intensities from both modes increase sharply at TC; therefore, both modes soften simultaneously. The first-principles calculations demonstrate that the M-point mode is electrostatically more preferable than the K-point mode and determines the eventual low-temperature structure, although these two modes are competing energetically. This competition is characteristic of BaAl2O4, which is ascribed to the structurally flexible network structure of this compound.

DOI： 10.1103/PhysRevB.93.134108

Novel charge ordering in the trimer iridium oxide BaIrO<inf>3</inf> 査読有り

Terasaki I., Ito S., Igarashi T., Asai S., Taniguchi H., Okazaki R., Yasui Y., Kobayashi K., Kumai R., Nakao H., Murakami Y.

Crystals 6 巻 ( 3 ) 2016年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Crystals

We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with face-shared Ir3O12 trimers, and have investigated the origin of the phase transition at 182 K by measuring resistivity, thermopower, magnetization and synchrotron X-ray diffraction. We propose a possible electronic model and transition mechanism, starting from a localized electron picture on the basis of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or one lattice site. The transition can be viewed as a transition from the Mott insulator phase to a kind of charge ordered insulator phase.

DOI： 10.3390/cryst6030027

Ferromagnetic Cluster Glass Phase Embedded in a Paramagnetic and Metallic Host in Non-Uniform Magnetic System CaRu1−xScxO3

Yamamoto Takafumi D., Kotani Atsuhiro, Nakajima Hiroshi, Okazaki Ryuji, Taniguchi Hiroki, Mori Shigeo, Terasaki Ichiro

Journal of the Physical Society of Japan 85 巻 ( 3 ) 頁： 34711 - 34711 2016年3月

High temperature stability of the dielectric and insulating properties of Ca(Ti, Zr)SiO<inf>5</inf> ceramics 査読有り

Kimura J., Taniguchi H., Iijima T., Shimizu T., Yasui S., Itoh M., Funakubo H.

Applied Physics Letters 108 巻 ( 6 ) 2016年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Letters

Useful dielectric properties for high-temperature ceramic capacitors are demonstrated in a non-perovskite oxide, Ca(Ti0.85 Zr0.15)SiO5, which is mainly composed of one-dimensional chains of oxygen octahedra that are mutually linked by SiO4 tetrahedra. Its dielectric constant and low temperature coefficient of capacitance were found to be 43 and -102 ppm/K, respectively, over the wide temperature range of 300-780 K. The high insulating performance was also indicated by the high resistivity, exceeding 1011 Ω cm up to 523 K. The systematic dielectric measurements for Ca(Ti1-x Zrx)SiO5 as functions of the composition and temperature indicate that the suppression of the anti-ferroelectric phase transition of CaTiSiO5 by Zr4+-substitution is a key to improve the temperature-stability and the high-resistivity in Ca(Ti1-x Zrx)SiO5. The present results shed light on the development of a designing principle for ceramic capacitors for the high-temperature use.

DOI： 10.1063/1.4941803

Optical conductivity of layered calcium cobaltate Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> 査読有り

Tanabe K., Okazaki R., Taniguchi H., Terasaki I.

Journal of Physics Condensed Matter 28 巻 ( 8 ) 頁： 085601 2016年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physics Condensed Matter

We report the optical properties of layered calcium cobaltate, Ca3Co4O9, which is regarded as a promising candidate for use as a thermoelectric material. The optical conductivity shows three broad peaks related to the inter-band transition below 4 eV, which are quite similar to those in the spectra of NaxCoO2. This similarity implies that the CoO2 layer, which is an essential unit for both Ca3Co4O9 and NaxCoO2, is dominant in the energy band structure below 4 eV. In addition, we estimate the effective carrier number per Co site and find similarity between the CoO2 layers of Ca3Co4O9 and Na0.75CoO2, which is consistent with the similarity in their Seebeck coefficients. To discuss the contribution of the rocksalt-type Ca2CoO3 layer in Ca3Co4O9, we propose the concept of optical sheet conductivity in the layered materials and estimate its value in the Ca2CoO3 layer. A comparison with the spin-polarized band calculation of the LDA + Hubbard U formalism with U = 5 eV suggests that the Ca2CoO3 layer has the inter-band transition of 2.6 eV in the spin-down band structure. Evaluation of the valences of Co 3d orbitals indicates the existence of charge transfer from the Ca2CoO3 layer to the CoO2 layer and mixing of Co3+ and Co4+ in the CoO2 layer, which may be the origin of the large thermoelectric effect.

DOI： 10.1088/0953-8984/28/8/085601

Ferromagnetic cluster glass phase embedded in a paramagnetic and metallic host in non-uniform magnetic system CaRu<inf>1-x</inf>Sc<inf>x</inf>O<inf>3</inf> 査読有り

Yamamoto T., Kotani A., Nakajima H., Okazaki R., Taniguchi H., Mori S., Terasaki I.

Journal of the Physical Society of Japan 85 巻 ( 3 ) 頁： 034711 2016年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We have investigated both static and dynamic magnetic properties of polycrystalline CaRu1-xScxO3 system in order to clarify the role of Sc ions as a disorder for magnetic ordering. We have observed typical features of a ferromagnetic cluster glass state below around 40 K: (i) a broad, frequency-dependent peak in the ac magnetic susceptibility, (ii) a slow relaxation of the magnetization, and (iii) a continuous increase in the dc magnetic susceptibility in field cooling process. The composition dependence of characteristic parameters for the cluster glass state suggests that chemical segregation can hardly explain the clustering mechanism. We propose a possible picture that the ferromagnetic clusters are distributed uniformly and form the glassy state embedded in the paramagnetic and metallic host of CaRuO3.

DOI： 10.7566/JPSJ.85.034711

Heterovalent Pb-substitution in ferroelectric bismuth silicate Bi2SiO5 査読有り

Hiroki Taniguchi, Tomohiro Nakane, Takayuki Nagai, Chikako Moriyoshi, Yoshihiro Kuroiwa, Akihide Kuwabara, Masaichiro Mizumaki, Kiyofumi Nitta, Ryuji Okazaki, Ichiro Terasaki

JOURNAL OF MATERIALS CHEMISTRY C 4 巻 ( 15 ) 頁： 3168 - 3174 2016年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

Systematic tuning of the ferroelectric phase transition in Bi2SiO5 was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi2O2 layers, resulting in the nominal composition (Bi1-x Pb-3+(x)2+)(2)SiO5-x. The oxygen vacancies were found to induce local disordering of SiO4 tetrahedral chains, sandwiched between the Bi2O2 layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi2SiO5.

DOI： 10.1039/c6tc00584e

Heterovalent Pb-substitution in ferroelectric bismuth silicate Bi<inf>2</inf>SiO<inf>5</inf> 査読有り

Hiroki Taniguchi, Tomohiro Nakane, Takayuki Nagai, Chikako Moriyoshi, Yoshihiro Kuroiwa, Akihide Kuwabara, Masaichiro Mizumaki, Kiyofumi Nitta, Ryuji Okazaki, Ichiro Terasaki

Journal of Materials Chemistry C 4 巻 ( 15 ) 頁： 3168 - 3174 2016年

掲載種別：研究論文（学術雑誌）

© The Royal Society of Chemistry 2016. Systematic tuning of the ferroelectric phase transition in Bi2SiO5 was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi2O2 layers, resulting in the nominal composition (Bi1-x3+Pbx2+)2SiO5-x. The oxygen vacancies were found to induce local disordering of SiO4 tetrahedral chains, sandwiched between the Bi2O2 layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi2SiO5.

DOI： 10.1039/c6tc00584e

充填型ソーダライト酸化物(CaxSr1-x )8 (Al O2)12(WO4 )2 の広帯域顕微光散乱分光

片山大輔, 藤井康裕, 是枝聡肇, 谷口博基, 寺崎一郎

日本物理学会講演概要集 71 巻 ( 0 ) 頁： 2553 - 2553 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

現在, 世界的に鉛含有の物質を非鉛物質に置き換える動きが進んでいる. 人感センサなどに使用されている焦電素子では, 現在の鉛含有の物質(PZT)を凌駕する性能を示す候補物質として, 充填型ソーダライト酸化物(Ca_x_Sr_1-x_ )_8_ (Al O_2_)_12_ (WO_4_ )_2_ が提案されている. しかし, 本物質の物性については, 誘電率の温度依存性や相転移機構なども含めて未解明な点が多く残されている. そこで, 本研究では格子振動の観点からこれらの物性を理解すべく, 幅広い温度領域における広帯域顕微光散乱分光を行ったので報告する.

DOI： 10.11316/jpsgaiyo.71.2.0_2553

Effects of the Ir impurity on the thermodynamic and transport properties of Ba<inf>4</inf>Ru<inf>3</inf>O<inf>10</inf> 査読有り

Ca2RuO4の非線形ゼーベック効果

戸田康介, 田辺賢士, 谷口博基, 岡崎竜二, 中村文彦, 寺崎一郎

日本物理学会講演概要集 71 巻頁： 1859 - 1859 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

Ca_2_RuO_4_は室温付近で非線形な電気伝導現象が観測されている物質である。非線形伝導現象の観測における課題として、電流印加による自己発熱の効果がある。これまでに我々は電流通電状態でも適用可能な試料温度測定法を開発し、非線形伝導現象を捉えることに成功している。今回はこの温度計測法を用いることで電流通電下でのゼーベック係数の測定を行った。

DOI： 10.11316/jpsgaiyo.71.2.0_1859

還元LaAlO3における光誘電効果

永井隆之, 田辺賢士, 寺崎一郎, 桑原彰秀, 谷口博基

日本物理学会講演概要集 71 巻頁： 2514 - 2514 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

昨年度我々は、LaAlO_3_にZnを置換したZn:LaAlO_3_において本質的な光誘電効果を報告した。本研究では、この本質的な光誘電効果の機構を明らかにするために、窒素還元雰囲気中で焼成した還元LaAlO_3_を作製し、光照射下での誘電率測定を行った。その結果、還元LaAlO_3_でもZn:LaAlO_3_と同様の本質的な光誘電効果を観測した。講演では、大気中で焼成したLaAlO_3_での結果と合わせて、この系で観測された本質的な光誘電効果の機構について議論する。

DOI： 10.11316/jpsgaiyo.71.2.0_2514

新規量子磁性体Ba3Zn1Ru2O9にドープされたCoの超低温磁化率

原佑樹, 松下琢, 和田信雄, 五十嵐太一, 谷田貝亮, 田辺賢士, 谷口博基, 寺崎一郎

日本物理学会講演概要集 71 巻頁： 1494 - 1494 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

我々は量子スピン液体状態の可能性が指摘されているBa_3_Zn_1_Ru_2_O_9_のZnを置換したCoの磁化および磁化率測定よりこの新奇な液体状態の検証を行なっている。これまでに観測した3％置換したCoの磁化率は、キュリーもしくはキュリー・ワイス的な磁化率と明らかに異なり、40mKまでゆるやかに増加した。講演ではこれらの結果を報告し液体状態の可能性について議論する。

DOI： 10.11316/jpsgaiyo.71.2.0_1494

共応答誘電体：光特性・機械特性・誘電特性をまたぐ新機能の創出に向けて

谷口博基

日本物理学会講演概要集 71 巻頁： 2587 - 2588 2016年

CaRu1-xScxO3の輸送特性における磁気ゆらぎの効果

山本貴史, 谷田貝亮, 田辺賢士, 岡崎竜二, 谷口博基, 安井幸夫, 井口敏, 佐々木孝彦, 寺崎一郎

日本物理学会講演概要集 71 巻頁： 1002 - 1002 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

常磁性物質CaRuO_3_はRuに対する不純物置換により強磁性を示す。これまで我々は、非磁性元素置換効果の研究から、この強磁性がCaRuO_3_の常磁性金属相と同時に存在する強磁性クラスターグラス状態に由来することを見出した。本研究では、これらの相関を調べることを目的として、ゼーベック係数と比熱の測定を行った。講演では、クラスター形成温度近傍における伝導電子に対する磁気ゆらぎの効果を中心に議論する。

DOI： 10.11316/jpsgaiyo.71.2.0_1002

CaPd3-xCuxO4(0≦x≦2.4)における輸送特性と磁気特性

三澤一輝, 田辺賢士, 谷口博基, 寺崎一郎

日本物理学会講演概要集 71 巻頁： 1000 - 1000 2016年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

CaPd_3_O_4_は、Pd^2+^の平面四配位構造をもつバンド絶縁体である。本研究では、PdをCuで置換した多結晶試料を作成し、Pdサイトを80%まで置換することに成功した。作成した試料について電気抵抗率、ゼーベック係数、及び磁化率の温度依存性を測定したところ、Cu置換によって基底状態がバンド絶縁体からモット絶縁体へと変化したことを示唆する結果が得られた。

DOI： 10.11316/jpsgaiyo.71.2.0_1000

Igarashi T., Okazaki R., Taniguchi H., Yasui Y., Terasaki I.

Journal of the Physical Society of Japan 84 巻 ( 9 ) 頁： 094601 2015年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Physical Society of Japan

We report the effects of Ir impurity on the physical properties of Ba4Ru3-xIrxO10 (0 ≤ x ≤ 0.5) which is composed of three face-shared RuO6 octahedra (Ru trimer). We discuss the origin of the unique electronic phase transition from paramagnetic metal to antiferromagnetic insulator at 105K in terms of hybridized orbitals of Ru 4d in the Ru trimer. From the magnetic susceptibility and the specific heat, the transition temperature is found to decrease more remarkably than is expected in typical diluted magnets and is hardly discernible at around x = 0.5, while the magnetic interaction only decreases slightly with x. This implies that the transition is not driven by magnetic interaction. In contrast, the hump due to the phase transition still remains in the Seebeck coefficient for x = 0.5, which means that the charge gap still remains as a short-range order. Since the charge gap originates from the 4d hybridization in the Ru trimer, intra-trimer charge transfer is likely to dominate the transition.

DOI： 10.7566/JPSJ.84.094601

Effects of the Ir Impurity on the Thermodynamic and Transport Properties of Ba4Ru3O10

Igarashi Taichi, Okazaki Ryuji, Taniguchi Hiroki, Yasui Yukio, Terasaki Ichiro

Journal of the Physical Society of Japan 84 巻 ( 9 ) 頁： 94601 - 94601 2015年9月

Strong anisotropy of ferroelectricity in lead-free bismuth silicate 査読有り

Seol Daehee, Taniguchi Hiroki, Hwang Jae-Yeol, Itoh Mitsuru, Shin Hyunjung, Kim Sung Wng, Kim Yunseok

NANOSCALE 7 巻 ( 27 ) 頁： 11561 - 11565 2015年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Nanoscale

Bismuth silicate (Bi2SiO5) was recently suggested as a potential silicate based lead-free ferroelectric material. Here, we show the existence of ferroelectricity and explore the strong anisotropy of local ferroelectricity using piezoresponse force microscopy (PFM). Domain structures are reconstructed using angle-resolved PFM. Furthermore, piezoresponse hysteresis loops and piezoelectric coefficients are spatially investigated at the nanoscale. The obtained results confirm the existence of ferroelectricity with strong c-axis polarization. These results could provide basic information on the anisotropic ferroelectricity in Bi2SiO5 and furthermore suggest its considerable potential for lead-free ferroelectric applications with silicon technologies.

DOI： 10.1039/c5nr03161c

Effects of element substitution on the pyroelectric phase transition of stuffed-tridymite-type BaZnGeO4 査読有り

Nagai Takayuki, Asai Shinichiro, Okazaki Ryuji, Terasaki Ichiro, Taniguchi Hiroki

SOLID STATE COMMUNICATIONS 219 巻頁： 12 - 15 2015年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Solid State Communications

Abstract Effects of element substitution on the phase transition between different pyroelectric phases of the stuffed-tridymite-type oxide, BaZnGeO4, are examined by dielectric measurements on BaZn1-xMxGeO4 (M=Ni, Co, and Mn) with x=0.05 and 0.10. The Ni2+-substitution is found to suppress strongly the phase transition, in marked contrast to the cases of Co2+ and Mn2+ that have only subtle influences on the transition temperature. Internal distortions of MO4 tetrahedra due to the Jahn-Teller effect might play a major role in the variation of transition temperature induced by the element substitution.

DOI： 10.1016/j.ssc.2015.06.011

Structural changes and microstructures of Ba1-x Sr (x) Al2O4 for 0 < x < 0.4

Tanaka E., Ishii Y., Tsukasaki H., Mori S., Osada M., Taniguchi H., Sato Y., Kubota Y.

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 66 巻 ( 9 ) 頁： 1355 - 1358 2015年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of the Korean Physical Society

We have investigated the structural changes and the microstructures of Ba1-xSrxAl2O4 for 0 < x < 0.4 by using transmission electron microscope (TEM) and synchrotron radiation powder X-ray diffraction experiments. The TEM experiments revealed the existence of a structural phase boundary at approximately x = 0.1, at which the superlattice reflection spots at the 1/2 0 0 -type positions change into diffuse streaks along three equivalent <110> directions in the hexagonal structure. In addition, real-space images of Ba1-xSrxAl2O4 for 0 < x < 0.4 reveal that BaAl2O4 should be characterized as a modulated structure with triple-q modulation vectors along the <110> directions and on the other hand, Ba1-xSrxAl2O4 for 0.1 < x < 0.4 be characterized as an intermediate (precursor) state with a rigid unit mode due to structural instability. These experimental results implied that the partial substitution of Sr2+ for Ba2+ should suppress a structural instability due to the AlO4 tetrahedral network and decrease the structural phase transition temperature.

DOI： 10.3938/jkps.66.1355

Non-uniform Magnetic System Driven by Non-magnetic Ion Substitution in CaRu1−xScxO3: Two-Component Analysis

Photo-Seebeck effect in ZnS 査読有り

Shiraishi Yuuka, Okazaki Ryuji, Taniguchi Hiroki, Terasaki Ichiro

JAPANESE JOURNAL OF APPLIED PHYSICS 54 巻 ( 3 ) 2015年3月

Non-uniform Magnetic System Driven by Non-magnetic Ion Substitution in CaRu1−xScxO3: Two-Component Analysis 査読有り

Takafumi D. Yamamoto, Ryuji Okazaki, Hiroki Taniguchi, Ichiro Terasaki

Journal of the Physical Society of Japan 84 巻 ( 1 ) 頁： 014708 2015年1月

Yamamoto Takafumi D., Okazaki Ryuji, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan 84 巻 ( 1 ) 頁： 14708 - 14708 2015年1月

広帯域光散乱分光によるリラクサー強誘電体のフラクタルダイナミクスの研究

是枝聡肇, 藤井康裕, 谷口博基

日本結晶学会誌 57 巻 ( 4 ) 頁： 219-225 2015年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report the broadband light-scattering spectroscopy of a single crystal of a prototypical relaxor ferroelectric, Pb（Mg1/3Nb2/3）O3. A self-similar, "power-law central peak" has been observed, indicating the presence of a fractal in the crystal. A strong correspondence exists between the temperature dependence of the power exponent, and that of the reported behaviors of "polar nanoregions", which consist of the fractal percolation cluster in the crystalline matrix of the material.

DOI： 10.5940/jcrsj.57.219

角度分解偏光ラマン分光による結晶性試料の振動モード解析

藤井康裕, 是枝聡肇, 清水荘雄, 谷口博基

日本結晶学会誌 57 巻 ( 5 ) 頁： 285-290 2015年

記述言語：英語掲載種別：研究論文（学術雑誌）

Phonon properties of lead titanate were investigated by measuring polarization-direction dependence of Raman intensities. Quantitative angle-resolved Raman spectroscopy is advantageous for detecting anisotropic nature of the sample material since that reflects the symmetry of vibrational modes. In this study, a broadband half-waveplate was utilized to establish high quantitativity, stability, and spatial reliability of the angle-resolved measurement.

DOI： 10.5940/jcrsj.57.285

Ruthenium oxide as a thermoelectric material: unconventional thermoelectric properties of Li2RuO3 査読有り

Ichiro Terasaki, Shuhei Abe, Yukio Yasui, Ryuji Okazaki, Hiroki Taniguchi

JOURNAL OF MATERIALS CHEMISTRY C 3 巻 ( 40 ) 頁： 10430 - 10435 2015年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ROYAL SOC CHEMISTRY

Ruthenium oxides are typical strongly correlated electron systems, where various ordering phenomena occur through delicate interplay among the charge, spin and orbital degrees of freedom. We propose that the thermoelectric properties can be improved by controlling such ordered phases in strongly correlated electron systems. Honeycomb Ru oxide Li2RuO3 is a prime example that exhibits a unique phase transition at 540 K with a charge gap. We have found that the ordered state can be modified by substituting the Ru site partially, and succeeded in increasing the thermopower by keeping the resistivity around the same value to enhance the power factor substantially.

DOI： 10.1039/c5tc01619c

Ruthenium oxide as a thermoelectric material: Unconventional thermoelectric properties of Li<inf>2</inf>RuO<inf>3</inf> 査読有り

Ichiro Terasaki, Shuhei Abe, Yukio Yasui, Ryuji Okazaki, Hiroki Taniguchi

Journal of Materials Chemistry C 3 巻 ( 40 ) 頁： 10430 - 10435 2015年

掲載種別：研究論文（学術雑誌）

© The Royal Society of Chemistry 2015. Ruthenium oxides are typical strongly correlated electron systems, where various ordering phenomena occur through delicate interplay among the charge, spin and orbital degrees of freedom. We propose that the thermoelectric properties can be improved by controlling such ordered phases in strongly correlated electron systems. Honeycomb Ru oxide Li2RuO3 is a prime example that exhibits a unique phase transition at 540 K with a charge gap. We have found that the ordered state can be modified by substituting the Ru site partially, and succeeded in increasing the thermopower by keeping the resistivity around the same value to enhance the power factor substantially.

DOI： 10.1039/c5tc01619c

21pCJ-2 ペロブスカイト型酸化物における強誘電性発現機構と新規強誘電体設計

谷口博基

日本物理学会講演概要集 70 巻 ( 0 ) 頁： 2698 - 2699 2015年

21aCH-3 PMN-PTの広帯域光散乱分光III

小川智大, 酒井洋徳, 片山大輔, 藤井康裕, 是枝聡肇, 谷口博基

日本物理学会講演概要集 70 巻頁： 2664 - 2664 2015年

21pBC-10 CaRu_<1-x>Sc_xO_3における磁性と輸送特性の相関

山本貴史, 岡崎竜二, 谷口博基, 寺崎一郎

日本物理学会講演概要集 70 巻頁： 2024 - 2024 2015年

21aCH-4 PMN-PT単結晶のラマン分光

藤井康裕, 小川智大, 酒井洋徳, 是枝聡肇, 谷口博基

日本物理学会講演概要集 70 巻頁： 2665 - 2665 2015年

22pCH-8 アルミネートゼオライトCa_8[Al_<12>O_<24>](WO_4)_2[CAW]における強誘電性

前田悠作, 森吉千佳子, 黒岩芳弘, 廣瀬左京, 岡崎竜二, 寺崎一郎, 谷口博基

日本物理学会講演概要集 70 巻頁： 2738 - 2738 2015年

Photo-transport properties of Pb2CrO5 single crystals 査読有り

P. S. Mondal, R. Okazaki, H. Taniguchi, I. Terasaki

Journal of Applied Physics 116 巻 ( 19 ) 頁： 193706 2014年11月

Structural changes and microstructures in stuffed tridymite-type compounds Ba1-xSrxAl2O4 査読有り

Tanaka Eri, Ishii Yui, Teukasaki Hirofumi, Taniguchi Hiroki, Mori Shigeo

JAPANESE JOURNAL OF APPLIED PHYSICS 53 巻 ( 9 ) 2014年10月

Structural Phase Transition and Microstructures in Stuffed Tridymite-Type Compounds; Ba(Al, Fe)(2)O-4

Mori S., Katsumura S., Ozaki T., Tanaka E., Ishii Y., Kurushima K., Kubota Y., Taniguchi H.

FERROELECTRICS 464 巻 ( 1 ) 頁： 116 - 121 2014年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ferroelectrics

We have investigated structural phase transition and changes of microstrucrtures in BaAl2O4 with the tridymite tetrahedral framework structure by transmission electron microscopy experiments in the temperature range between 100 K and 298 K. In our polycrystalline samples the transition from the paraelectric phase with the P6322 space group to the ferroelectric (FE) phase took place around 250 K, which ccompanie with the appearance of the modulated structure with the three equivalent modulation wave vectors, q = 1/2<100>. Real-space images revealed that the FE phase should consist of nanodomains with the 10 ∼ 20 nm size. In addition, it is revealed that partial substitution of Fe3+ for Al3+ in BaAl2O4 induced structural phase transition to themodulated structure with q = 1/3<110> around x ∼ 0.50 in Ba(Al 1-xFex)2O4.

DOI： 10.1080/00150193.2014.893160

Pseudogap Observed in the Charge Transport in the Thermoelectric Oxide Ca3−xBixCo4O9 Single Crystals

Pseudogap Observed in the Charge Transport in the Thermoelectric Oxide Ca3−xBixCo4O9 Single Crystals 査読有り

Yu-Chin Hsieh, Ryuji Okazaki, Hiroki Taniguchi, Ichiro Terasaki

Journal of the Physical Society of Japan 83 巻 ( 5 ) 頁： 054710 2014年5月

Hsieh Yu-Chin, Okazaki Ryuji, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan 83 巻 ( 5 ) 頁： 54710 - 54710 2014年5月

Electrical oscillation in SmS induced by a constant external voltage 査読有り

Takahashi H., Okazaki R., Taniguchi H., Terasaki I., Saito M., Imura K., Deguchi K., Sato N. K., Suzuki H. S.

PHYSICAL REVIEW B 89 巻 ( 19 ) 2014年5月

Raman Tensor Analysis of Crystalline Lead Titanate by Quantitative Polarized Spectroscopy 査読有り

Fujii Y., Noju M., Shimizu T., Taniguchi H., Itoh M., Nishio I.

FERROELECTRICS 462 巻 ( 1 ) 頁： 8 - 13 2014年4月

Hierarchical dielectric orders in layered ferroelectrics Bi2SiO5 査読有り

Kim Younghun, Kim Jungeun, Fujiwara Akihiko, Taniguchi Hiroki, Kim Sungwng, Tanaka Hiroshi, Sugimoto Kunihisa, Kato Kenichi, Itoh Mitsuru, Hosono Hideo, Takata Masaki

IUCRJ 1 巻 ( Pt 3 ) 頁： 160 - 164 2014年4月

Photo-induced change of dielectric response in BaCoSiO4 stuffed tridymite 査読有り

Taniguchi Hiroki, Moriwake Hiroki, Kuwabara Akihide, Okamura Takuma, Yamamoto Takafumi, Okazaki Ryuji, Itoh Mitsuru, Terasaki Ichiro

JOURNAL OF APPLIED PHYSICS 115 巻 ( 16 ) 2014年4月

Growth and characterization of Cu2ZnSn(SxSe1-x)(4) alloys grown by the melting method 査読有り

Nagaoka Akira, Yoshino Kenji, Taniguchi Hiroki, Taniyama Tomoyasu, Kakimoto Koichi, Miyake Hideto

JOURNAL OF CRYSTAL GROWTH 386 巻頁： 204 - 207 2014年1月

Epitaxial growth of metastable multiferroic AlFeO3 film on SrTiO3 (111) substrate 査読有り

Hamasaki Yosuke, Shimizu Takao, Taniguchi Hiroki, Taniyama Tomoyasu, Yasui Shintaro, Itoh Mitsuru

APPLIED PHYSICS LETTERS 104 巻 ( 8 ) 2014年

27aCJ-6 SmSにおける定電場下での電流振動現象(27aCJ 希土類化合物(磁性・重い電子状態・価数揺動など),領域8(強相関系))

高橋英史, 岡崎竜二, 谷口博基, 寺崎一郎, 斉藤真衣, 井村敬一郎, 出口和彦, 佐藤憲昭

日本物理学会講演概要集 69.1.3 巻 ( 0 ) 頁： 550 2014年

8aBG-7 バリスティックなフォノン伝導に起因したFeSb_2単結晶の巨大ゼーベック効果(8aBG 遷移金属化合物2(金属酸化物・金属間化合物),領域8(強相関系))

高橋英史, 岡崎竜二, 谷口博基, 寺崎一郎

日本物理学会講演概要集 69.2.3 巻 ( 0 ) 頁： 350 2014年

8aBA-4 Ba_3ZnRu_2O_9のZnサイト置換効果(8aBA 量子スピン(2次元系),領域3(磁性))

五十嵐太一, 岡崎竜二, 谷口博基, 寺崎一郎

日本物理学会講演概要集 69.2.3 巻 ( 0 ) 頁： 285 2014年

8aAF-13 充填トリジマイト型強誘電体BaZnGeO_4の元素置換効果(8aAF 誘電体(ドメイン・相転移),領域10(構造物性(誘電体,格子欠陥,X線・粒子線,フォノン)))

永井隆之, 浅井晋一郎, 岡崎竜二, 寺崎一郎, 谷口博基

日本物理学会講演概要集 69.2.4 巻 ( 0 ) 頁： 693 2014年

7aPS-2 PMN-PTの広帯域光散乱分光II(7aPS 領域10ポスターセッション(誘電体・格子欠陥・中性子),領域10(構造物性(誘電体,格子欠陥,X線・粒子線,フォノン)))

小川智大, 酒井洋徳, 藤井康裕, 是枝聡肇, 谷口博基

日本物理学会講演概要集 69.2.4 巻 ( 0 ) 頁： 680 2014年

Photo-Seebeck effect in tetragonal PbO single crystals 査読有り

Mondal P. S., Okazaki R., Taniguchi H., Terasaki I.

JOURNAL OF APPLIED PHYSICS 114 巻 ( 17 ) 2013年11月

X-ray Crystal Structure Analysis and Ru Valence of Ba4Ru3O10Single Crystals

Igarashi Taichi, Nogami Yoshio, Klein Yannick, Rousse Gwenaelle, Okazaki Ryuji, Taniguchi Hiroki, Yasui Yukio, Terasaki Ichiro

Journal of the Physical Society of Japan 82 巻 ( 10 ) 頁： 104603 - 104603 2013年10月

X-ray Crystal Structure Analysis and Ru Valence of Ba4Ru3O10Single Crystals 査読有り

Taichi Igarashi, Yoshio Nogami, Yannick Klein, Gwenaelle Rousse, Ryuji Okazaki, Hiroki Taniguchi, Yukio Yasui, Ichiro Terasaki

Journal of the Physical Society of Japan 82 巻 ( 10 ) 頁： 104603 2013年10月

Confocal micro-Raman imaging on 180 degrees-domain structure in periodically poled stoichiometric LiNbO3 査読有り

Taniguchi Hiroki, Fujii Yasuhiro, Itoh Mitsuru

大日本窯業協會雑誌 121 巻 ( 1416 ) 頁： 579 - 582 2013年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

A domain structure in periodically poled stoichiometric LiNbO3 was observed by confocal micro-Raman scanning spectroscopy. The 180°-domain, which is nominally invisible by Raman scattering due to equivalency of Raman selection rule for adjacent domains, was clearly visualized with a spatial resolution of 460 nm. At domain walls, an enhancement of Raman intensity was observed in optical modes that are closely related to the Nb–O bond, while there was no significant change in Li-ion related modes. Nb–O covalent bonds would be deformed by opposite ferroelectric displacements of ions across domain walls, to modify an electric polarizability of the Nb-ion related modes.

DOI： 10.2109/jcersj2.121.579

Ultrafast Real Space Dynamics of Photoexcited State in a Layered Perovskite-Type Spin Crossover Oxide La1.5Sr0.5CoO4

Ferroelectricity Driven by Twisting of Silicate Tetrahedral Chains 査読有り

Taniguchi Hiroki, Kuwabara Akihide, Kim Jungeun, Kim Younghun, Moriwake Hiroki, Kim Sungwng, Hoshiyama Takuya, Koyama Tsukasa, Mori Shigeo, Takata Masaki, Hosono Hideo, Inaguma Yoshiyuki, Itoh Mitsuru

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 52 巻 ( 31 ) 頁： 8088 - 8092 2013年7月

Okimoto Yoichi, Egawa Tsugumi, Fukaya Ryo, Matsubara Yoshitaka, Yamada Yuki, Yamaya Nao, Ishikawa Tadahiko, Onda Ken, Koshihara Shin-ya, Taniguchi Hiroki, Itoh Mitsuru, Isayama Akira, Sasagawa Takao

Journal of the Physical Society of Japan 82 巻 ( 7 ) 頁： 74721 - 74721 2013年7月

Growth and characterization of Cu2ZnSnS4 single crystals 査読有り

Nagaoka Akira, Yoshino Kenji, Taniguchi Hiroki, Taniyama Tomoyasu, Kakimoto Koichi, Miyake Hideto

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 210 巻 ( 7 ) 頁： 1328 - 1331 2013年7月

Ultrafast Real Space Dynamics of Photoexcited State in a Layered Perovskite-Type Spin Crossover Oxide La1.5Sr0.5CoO4 査読有り

Yoichi Okimoto, Tsugumi Egawa, Ryo Fukaya, Yoshitaka Matsubara, Yuki Yamada, Nao Yamaya, Tadahiko Ishikawa, Ken Onda, Shin-ya Koshihara, Hiroki Taniguchi, Mitsuru Itoh, Akira Isayama, Takao Sasagawa

Journal of the Physical Society of Japan 82 巻 ( 7 ) 頁： 074721 2013年7月

Electric-voltage control of magnetism in Fe/BaTiO3 heterostructured multiferroics 査読有り

Venkataiah G., Wada E., Taniguchi H., Itoh M., Taniyama T.

JOURNAL OF APPLIED PHYSICS 113 巻 ( 17 ) 頁： 17C701/1 - 3 2013年5月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Journal of Applied Physics

Electric field (E) control of the magnetic anisotropy and coercivity (HC) of a Fe film in Fe/BaTiO3 (BTO) is demonstrated at room temperature in the tetragonal phase of BTO. Polarizing microscopy and x-ray diffraction analysis of BTO (001) surface show distinctly two different regions; one with a1, a2 and c domains separated by 180° and 90° domain boundaries (DBs) (region 1) and the other with a1 domains separated by 180° DBs (region 2). The Fe film on region 1 shows complex magnetic anisotropy with the net magnetic easy axis in between [100] and [110] directions of BTO, while the magnetic anisotropy in region 2 exhibits two fold symmetry with an easy axis along [100]. In applied electric field (±10 kV/cm), the magnetic easy axis of the Fe film in region 1 is switched to the [110] direction of BTO, whereas in region 2 it stays unaffected. The HC versus E curves in region 1 show a butterfly-like behavior, while in region 2 no changes are observed. Also, the HC measured in E ±10 kV/cm at different magnetic field orientations shows dramatic changes in region 1 compared to region 2. The observed electric field dependent magnetic response in both regions can be understood based on the DBs modifications and associated strain effects. © 2013 American Institute of Physics.

DOI： 10.1063/1.4793511

Structural Modification and Domain Structure in a BaTiO₃ Film on (110) SrTiO₃

その他リンク： http://orcid.org/0000-0003-3683-5416

Comparative study of phase transitions in BaTiO3 thin films grown on (001)- and (110)-oriented SrTiO3 substrate 査読有り

Shimizu Takao, Suwama Dai, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru

JOURNAL OF PHYSICS-CONDENSED MATTER 25 巻 ( 13 ) 2013年4月

6 巻 ( 1 ) 頁： "015803-1"-"015803-3" 2013年1月

Structural Modification and Domain Structure in a BaTiO3 Film on (110) SrTiO3 査読有り

Shimizu Takao, Suwama Dai, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru

APPLIED PHYSICS EXPRESS 6 巻 ( 1 ) 2013年1月

SrTiO3（110）基板上に成長させたBaTiO3薄膜における特異な構造

清水荘雄, 谷口博基, 谷山智康, 伊藤満

日本結晶学会誌 55 巻 ( 5 ) 頁： 290 - 295 2013年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本結晶学会

An unconventional pseudo-tetragonal crystal structure is found in a BaTiO3 epitaxial thin film grown on a （110）SrTiO3 substrate. The unique crystal structure of the BaTiO3 film, which is markedly different from the bulk tetragonal structure, is caused by the nearly uniaxial strain due to the different strain relaxation along ［001］ and ［110］ axes.

DOI： 10.5940/jcrsj.55.290

25pDB-11 Photo-Seebeck properties of Pb_2CrO_5 crystals

High photodegradation efficiency of Rhodamine B catalyzed by bismuth silicate nanoparticles 査読有り

Duan Jiao, Liu Yan, Pan Xiuhong, Zhang Yubo, Yu Jianding, Nakajim Kiyotaka, Taniguchi Hiroki

CATALYSIS COMMUNICATIONS 39 巻頁： 65 - 69 2013年

Mondal P.S., Okazaki R., Taniguchi H., Terasaki I.

日本物理学会講演概要集 68.2.4 巻 ( 0 ) 頁： 650 2013年

28aEB-3 パイロクロア酸化物Dy_2Ru_2O_7の磁気誘電性(パイロクロア系,領域8(強相関系分野:高温超伝導,強相関f電子系など))

岡村卓真, 岡崎竜二, 安井幸夫, 谷口博基, 寺崎一郎

日本物理学会講演概要集 68.2.3 巻 ( 0 ) 頁： 583 2013年

26aPS-144 定量的偏光ラマン分光法による単結晶試料のラマンテンソル解析(26aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

藤井康裕, 能重昌嗣, 清水荘雄, 谷口博基, 伊藤満, 西尾泉

日本物理学会講演概要集 68.1.4 巻 ( 0 ) 頁： 1020 2013年

27aXZB-8 リラクサーPMN-PTにおけるフラクタルダイナミクス : 広帯域光散乱分光(27aXZB 誘電体(水素結合系,TGS他,リラクサー),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

是枝聡肇, 齊官清四郎, 谷口博基, 伊藤満

日本物理学会講演概要集 68.1.4 巻 ( 0 ) 頁： 1033 2013年

26pEN-6 化学結合から見たペロブスカイト型酸化物における強誘電性発現機構と新強誘電体設計への展望(26pEN 領域10,領域7,領域8合同シンポジウム:誘電体の電子構造と最近のトピックス,領域8(強相関系:高温超伝導,強相関f電子系など))

谷口博基

日本物理学会講演概要集 68.1.3 巻 ( 0 ) 頁： 581 2013年

26pEN-6 化学結合から見たペロブスカイト型酸化物における強誘電性発現機構と新強誘電体設計への展望(26pEN 領域10,領域7,領域8合同シンポジウム:誘電体の電子構造と最近のトピックス,領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

谷口博基

日本物理学会講演概要集 68.1.4 巻 ( 0 ) 頁： 1022 2013年

Fractal Dynamics in a Single Crystal of a Relaxor Ferroelectric 査読有り

Koreeda Akitoshi, Taniguchi Hiroki, Saikan Seishiro, Itoh Mitsuru

PHYSICAL REVIEW LETTERS 109 巻 ( 19 ) 頁： 197601 2012年11月

第一原理計算と高精度実験の連携による強誘電体材料研究査読有り

森分博紀, 谷口博基, 橋本保

応用物理 81 巻 ( 9 ) 頁： 760 - 764 2012年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人応用物理学会

第一原理計算は近年大きく発展し，現実的な材料研究に広く活用される段階になっている．本稿では，この第一原理計算と高精度な実験とを連携させることにより強誘電体の相転移機構，強誘電相の構造について研究した結果を解説する．

DOI： 10.11470/oubutsu.81.9_760

Growth of Cu2ZnSnSe4 single crystals from Sn solutions 査読有り

Nagaoka Akira, Yoshino Kenji, Taniguchi Hiroki, Taniyama Tomoyasu, Miyake Hideto

JOURNAL OF CRYSTAL GROWTH 354 巻 ( 1 ) 頁： 147 - 151 2012年9月

Ionic liquid-mediated epitaxy of high-quality C-60 crystallites in a vacuum 査読有り

Takeyama Yoko, Maruyama Shingo, Taniguchi Hiroki, Itoh Mitsuru, Ueno Keiji, Matsumoto Yuji

CRYSTENGCOMM 14 巻 ( 15 ) 頁： 4939 - 4945 2012年8月

Origin of the dielectric response in Ba0.767Ca0.233TiO3 査読有り

Shimizu Takao, Fu Desheng, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru

APPLIED PHYSICS LETTERS 100 巻 ( 10 ) 2012年3月

Preparation of Cu2ZnSnS4 single crystals from Sn solutions 査読有り

Nagaoka Akira, Yoshino Kenji, Taniguchi Hiroki, Taniyama Tomoyasu, Miyake Hideto

JOURNAL OF CRYSTAL GROWTH 341 巻 ( 1 ) 頁： 38 - 41 2012年2月

Effect of Ca-Substitution on CdTiO3 Studied by Raman Scattering and First Principles Calculations 査読有り

Taniguchi Hiroki, Soon Hwee Ping, Moriwake Hiroki, Shan Yue Jin, Itoh Mitsuru

FERROELECTRICS 426 巻 ( 1 ) 頁： 268 - 273 2012年1月

ペロブスカイト型酸化物における強誘電性の起源

谷口博基, 伊藤満, 森分博紀, 単躍進

日本結晶学会誌 54 巻 ( 5 ) 頁： 276 - 281 2012年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：日本結晶学会

An Origin of ferroelectricity in Perovskite-type oxides is discussed from a viewpoint of relation between lattice dynamics and chemical bonding state, through comprehensive study of a Ca-substitution effect on the ferroelectricity in CdTiO3. The result indicates covalency of constituent elements plays an important role on the ferroelectricity in the perovskite-type oxides.

DOI： 10.5940/jcrsj.54.276

Growth of KH2PO4 Single Crystal with an Artificial Isotope Gradient 査読有り

Osada K., Taniguchi H., Taniyama T., Itoh M.

FERROELECTRICS 440 巻 ( 1 ) 頁： 25 - 30 2012年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Ferroelectrics

KH2PO4 (KDP) single crystals internally including an artificial isotope gradient are grown by a controlled solution-recrystallization method. The deuteron exchange rate of KDP single crystal is spatially tailored through crystal growth in a KD2PO4 (DKDP) saturated solution, where the deuteron concentration decreases with time. The position dependence of the deuteron concentration was precisely determined with confocal micro-Raman scanning giving a change in the Raman spectrum as a proof. The result indicates that the deuteron concentration continuously varies from 77 % to 7 % within 100 microns. Copyright © Taylor & Francis Group, LLC.

DOI： 10.1080/00150193.2012.743786

25aPS-10 広帯域波長板を用いた定量的偏光ラマン分光(25aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

その他リンク： http://orcid.org/0000-0003-3683-5416

イルメナイト型MgTiO3薄膜の蛍光特性

浜嵜容丞, 清水荘雄, 谷口博基, 谷山智康, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2012 巻 ( 0 ) 頁： 192 - 192 2012年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

本研究では、Pulsed Laser Deposition (PLD)法によって合成したイルメナイト型MgTiO3単結晶薄膜の蛍光特性を調べた。その結果、製膜時のターゲット－基板間距離を減少させるにつれて、605nm近傍にバルク試料では見られないブロードな蛍光成分が成長することが分かった。この蛍光特性の起源を欠陥化学的観点より議論する。

DOI： 10.14853/pcersj.2012S.0.192.0

藤井康裕, 能重昌嗣, 清水荘雄, 谷口博基, 伊藤満, 西尾泉

日本物理学会講演概要集 67.1.4 巻 ( 0 ) 頁： 997 2012年

25aPS-9 Bi_2WO_6の定量的偏光ラマン分光(25aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

能重昌嗣, 藤井康裕, 清水荘雄, 谷口博基, 符徳勝, 伊藤満, 西尾泉

日本物理学会講演概要集 67.1.4 巻 ( 0 ) 頁： 997 2012年

Growth of Cu2ZnSnS4 Single Crystal by Traveling Heater Method 査読有り

Nagaoka Akira, Yoshino Kenji, Taniguchi Hiroki, Taniyama Tomoyasu, Miyake Hideto

JAPANESE JOURNAL OF APPLIED PHYSICS 50 巻 ( 12 ) 2011年12月

Mechanism for suppression of ferroelectricity in Cd<inf>1-x</inf>Ca <inf>x</inf>TiO<inf>3</inf> 査読有り

Hiroki Taniguchi, Hwee Ping Soon, Takao Shimizu, Hiroki Moriwake, Yue Jin Shan, Mitsuru Itoh

Physical Review B - Condensed Matter and Materials Physics 84 巻 ( 17 ) 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

A mechanism for cation-substitution-induced suppression of ferroelectricity in a perovskite-type ferroelectric oxide, CdTiO3, has been elucidated in terms of the relationship between the covalency and the lattice dynamics. Raman scattering experiments and first-principles calculations clarified that a change in the covalency of Cd sites due to Ca substitution selectively decreases the frequencies of the modes associated with octahedral rotations whose axes are perpendicular to the spontaneous polarization direction. The resulting destabilization of zigzag octahedral chains synchronizes the hardening of the ferroelectric soft mode, which suppresses the ferroelectricity. This result enhances our understanding of the relationship between local chemical bonds and macroscopic ferroelectricity. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.84.174106

Mechanism for suppression of ferroelectricity in Cd1-xCaxTiO3 査読有り

Hiroki Taniguchi, Hwee Ping Soon, Takao Shimizu, Hiroki Moriwake, Yue Jin Shan, Mitsuru Itoh

PHYSICAL REVIEW B 84 巻 ( 17 ) 2011年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

DOI： 10.1103/PhysRevB.84.174106

Enhancement of Quantum Ferroelectricity in SrTi^<18>O_3 Thin Film

High-throughput CW-IR laser deposition and laser microscope imaging of binary ionic liquids in vacuum 査読有り

Maruyama Shingo, Taniguchi Hiroki, Takeyama Yoko, Itoh Mitsuru, Matsumoto Yuji

SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 12 巻 ( 5 ) 頁： 054204 2011年10月

Fujii Yasuhiro, Maeda Yuki, Katayama Masao, TANIGUCHI Hiroki, TAKASHIMA Hiroshi, ITOH Mitsuru, MATSUMOTO Yuji

Applied physics express 4 巻 ( 9 ) 頁： "091501 - 1"-"091501-3" 2011年9月

Spontaneous polarization estimation from the soft mode in strain-free epitaxial polar axis-oriented Pb(Zr,Ti)O-3 thick films with tetragonal symmetry (vol 98, 141914, 2011) 査読有り

Ehara Yoshitaka, Utsugi Satoru, Nakajima Mitsumasa, Yamada Tomoaki, Iijima Takashi, Taniguchi Hiroki, Itoh Mitsuru, Funakubota Hiroshi

APPLIED PHYSICS LETTERS 99 巻 ( 12 ) 2011年9月

First-principles calculations of lattice dynamics in CdTiO<inf>3</inf> and CaTiO<inf>3</inf>: Phase stability and ferroelectricity 査読有り

Hiroki Moriwake, Akihide Kuwabara, Craig A.J. Fisher, Hiroki Taniguchi, Mitsuru Itoh, Isao Tanaka

Physical Review B - Condensed Matter and Materials Physics 84 巻 ( 10 ) 頁： 104114 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

First-principles calculations of various phases of CdTiO3 carried out with the aim of obtaining insights into the mechanism of the ferroelectric phase transition and the structure of the low-temperature ferroelectric phase are reported. The results indicate that the preferred symmetry of the low-temperature phase is Pna21, rather than P2 1ma, corresponding to a small relative shift of the Ti and O ions in the paraelectric Pnma phase with the polarization axis parallel to the long axis. Calculated phonon dispersion curves show a distinct soft mode at the Γ point of the Pnma phase, which vanishes in the Pna21 phase, confirming that the transition to the ferroelectric phase is of the soft-mode displacive type. Calculations of perovskite CaTiO3, which also has an orthorhombic Pnma structure at room temperature but, unlike CdTiO3, does not exhibit a ferroelectric phase transition down to 4.2 K, were also carried out to help characterize the factors controlling ferroelectric phase transitions in perovskite titanates. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.84.104114

Enhancement of Quantum Ferroelectricity in (SrTiO3)-O-18 Thin Film 査読有り

Fujii Yasuhiro, Maeda Yuki, Katayama Masao, Taniguchi Hiroki, Takashima Hiroshi, Itoh Mitsuru, Matsumoto Yuji

APPLIED PHYSICS EXPRESS 4 巻 ( 9 ) 2011年9月

First-principles calculations of lattice dynamics in CdTiO3 and CaTiO3: Phase stability and ferroelectricity 査読有り

Hiroki Moriwake, Akihide Kuwabara, Craig A. J. Fisher, Hiroki Taniguchi, Mitsuru Itoh, Isao Tanaka

PHYSICAL REVIEW B 84 巻 ( 10 ) 2011年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

First-principles calculations of various phases of CdTiO3 carried out with the aim of obtaining insights into the mechanism of the ferroelectric phase transition and the structure of the low-temperature ferroelectric phase are reported. The results indicate that the preferred symmetry of the low-temperature phase is Pna2(1), rather than P2(1)ma, corresponding to a small relative shift of the Ti and O ions in the paraelectric Pnma phase with the polarization axis parallel to the long axis. Calculated phonon dispersion curves show a distinct soft mode at the Gamma point of the Pnma phase, which vanishes in the Pna2(1) phase, confirming that the transition to the ferroelectric phase is of the soft-mode displacive type. Calculations of perovskite CaTiO3, which also has an orthorhombic Pnma structure at room temperature but, unlike CdTiO3, does not exhibit a ferroelectric phase transition down to 4.2 K, were also carried out to help characterize the factors controlling ferroelectric phase transitions in perovskite titanates.

DOI： 10.1103/PhysRevB.84.104114

リラクサーの謎の解明に向けて : 分極,分光測定と電顕観察より(最近の研究から)

Switching of the symmetry of magnetic anisotropy in Fe/BaTiO3 heterostructures 査読有り

Shirahata Y., Nozaki T., Venkataiah G., Taniguchi H., Itoh M., Taniyama T.

APPLIED PHYSICS LETTERS 99 巻 ( 2 ) 頁： 022501/1 - 3 2011年7月

Ferroelectricity and electromechanical coupling in (1-x)AgNbO3-xNaNbO(3) solid solutions 査読有り

Fu Desheng, Arioka Takahiro, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru

APPLIED PHYSICS LETTERS 99 巻 ( 1 ) 2011年7月

符徳勝, 谷口博基, 伊藤満, 森茂生

日本物理学会誌 66 巻 ( 4 ) 頁： 270 - 276 2011年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

リラクサー(relaxor)が示す特異な誘電特性に関しては長年議論されてきたが,その本質的な発現機構は未解明のままである.本研究では,代表的なリラクサー物質であるPb(Mg_<1/3>Nb_<2/3>)O_3(PMN)を対象とし,分極測定,ラマン分光,及び透過型電子顕微鏡観察の実験結果を総合的に解析した結果,以下の結論を得た:(1)PMNにおける広範な温度領域にわたる巨大な誘電応答は分極ドメインの応答に由来する.(2)PMNは本質的にはT_c〜225Kの強誘電体である.(3)強誘電相において,ナノサイズのドメインは互いにマイクロメートルオーダーの範囲で相互作用し,全体としてより大きなドメイン構造を形成する.これらの結果より,リラクサーという複雑系物質の物理像がより明確になった.ここで明らかになった「ドメイン構造の多重スケール不均一性」とも言うべき階層的構造が,今後の巨大応答物質開発に対して新たな方向性を与えることに期待したい.

DOI： 10.11316/butsuri.66.4_270

PLD法によるLiNbO3型遷移金属複酸化物薄膜の作製および磁性と強誘電性

Raman scattering study of the soft mode in Pb(Mg1/3Nb2/3)O-3 査読有り

Taniguchi Hiroki, Itoh Mitsuru, Fu Desheng

JOURNAL OF RAMAN SPECTROSCOPY 42 巻 ( 4 ) 頁： 706 - 714 2011年4月

Spontaneous polarization estimation from the soft mode in strain-free epitaxial polar axis-oriented Pb(Zr,Ti)O-3 thick films with tetragonal symmetry 査読有り

Ehara Yoshitaka, Utsugi Satoru, Nakajima Mitsumasa, Yamada Tomoaki, Iijima Takashi, Taniguchi Hiroki, Itoh Mitsuru, Funakubo Hiroshi

APPLIED PHYSICS LETTERS 98 巻 ( 14 ) 2011年4月

Ferroelectricity of Li-doped silver niobate (Ag, Li)NbO3 査読有り

Fu Desheng, Endo Makoto, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru, Koshihara Shin-ya

JOURNAL OF PHYSICS-CONDENSED MATTER 23 巻 ( 7 ) 頁： 075901 2011年2月

Power-Law Quasielastic Light Scattering Observed in Relaxor Pb(Mg1/3Nb2/3)O-3 査読有り

Koreeda Akitoshi, Saikan Seishiro, Taniguchi Hiroki, Itoh Mitsuru

FERROELECTRICS 415 巻 ( 1 ) 頁： 24 - 28 2011年

濱嵜容丞, 清水荘雄, 谷口博基, 谷山智康, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2011 巻 ( 0 ) 頁： 626 - 626 2011年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

高圧安定相であるLiNbO3型酸化物をPLD法で初めて作製し、その構造と物性を評価した。MnTiO3、FeTiO3ともエピタキシャル薄膜が得られ、その磁性と、強誘電性を調べた。

DOI： 10.14853/pcersj.2011F.0.626.0

ラマン散乱によるCdTiO3におけるCa置換効果の研究

谷口博基, Hwee Ping Soon, 森分博紀, 単躍進, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2011 巻 ( 0 ) 頁： 320 - 320 2011年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

ペロブスカイト型酸化物強誘電体CdTiO3は約８０Kで強誘電性相転移を示し、CdをCaで部分的に置換することでその強誘電性が抑制される。本研究ではCa置換による共有結合性の変化が格子振動に及ぼす効果をラマン散乱により系統的に研究し、Ca置換によるCdTiO3の強誘電性抑制のメカニズムを明らかにしたので、その結果を報告する。

DOI： 10.14853/pcersj.2011F.0.320.0

基板方位の異なるSrTiO3上に作成したBaTiO3薄膜のドメイン構造解析

清水荘雄, 諏訪間大, 谷口博基, 谷山智康, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2011 巻 ( 0 ) 頁： 286 - 286 2011年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

モルフォトロピック相境界などに代表されるように、強誘電体においては応答物性がドメイン構造や結晶構造に大きく左右されることが知られている。特に強誘電体薄膜においては基板から受ける2次元的な応力によってこれらの構造が変化するため、結晶構造やドメイン構造を積極的に制御する試みが行われている。　本研究ではパルスレーザー堆積(PLD法）によってBaTiO3（BTO)薄膜を基板方位の異なるSrTiO3（STO)上に成長させ、そのドメイン構造を圧電応答顕微鏡（PFM)によって評価したので、これを報告する。　STO(100)上に成長させたBTO薄膜は面直方向のみの分極成分がPFMによって観測され、シングルドメインとなっている。それに対してSTO(110)及び(111)上に成長させたBTO薄膜においては面直方向の分極は揃っているのに対して、面内方向の分極成分がストライプ状のドメインを構成していることが分かった。

DOI： 10.14853/pcersj.2011F.0.286.0

21pGN-5 CdTiO_3の強誘電性におけるCa置換の効果(21pGN リラクサー・光散乱,領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

谷口博基, 森分博紀, 単躍進, 清水荘雄, 伊藤満

日本物理学会講演概要集 66.2.4 巻 ( 0 ) 頁： 974 2011年

26aPS-122 (Ba_<1-x>Ca_x)TiO_3の透過型電子顕微鏡における微細構造評価(26aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

小山司, 尾崎友厚, 森茂生, 符徳勝, 清水荘雄, 谷口博基, 伊藤満

日本物理学会講演概要集 66.1.4 巻 ( 0 ) 頁： 972 2011年

26aPS-117 酸化物強誘電体の偏光ラマン分光(26aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

藤井康裕, 能重昌嗣, 西尾泉, 清水荘雄, 谷口博基, 伊藤満

日本物理学会講演概要集 66.1.4 巻 ( 0 ) 頁： 970 2011年

26aPS-113 強誘電体Ba_<1-x>Ca_xTiO_3における相転移機構(26aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

清水荘雄, 符徳勝, 谷口博基, 谷山智康, 伊藤満

日本物理学会講演概要集 66.1.4 巻 ( 0 ) 頁： 969 2011年

26aPS-112 擬一次元鎖状ペロブスカイトK_2(NbO)_2Si_4O_<12>の合成と物性評価(26aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

谷口博基, 森分博紀, 伊藤満

日本物理学会講演概要集 66.1.4 巻 ( 0 ) 頁： 969 2011年

25pTM-3 リラクサーPb(Mg_<1/3>Nb_<2/3>)O_3の低周波数領域光散乱分光(III)(25pTM リラクサー,酸化物系,ペロブスカイト,領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

是枝聡肇, 齊官清四郎, 谷口博基, 伊藤満, 森茂生

日本物理学会講演概要集 66.1.4 巻 ( 0 ) 頁： 960 2011年

Ferroelectricity of Li-doped Silver Niobate (Ag,Li)NbO_3 査読有り

谷口博基, 谷山智康

Journal of Physics : Condensed Matter 23 巻頁： 0759011 - 7 2011年

Spontaneous Polarization Estimation from the Soft Mode in Strain-Free Epitaxial Polar Axis-Oriented Pb(Zr, Ti)O_3 Thick Films with Tetragonal Symmetry 査読有り

谷口博基

Applied Physics Letters (in press) 巻 2011年

リラクサーの謎の解明に向けて-分極,分光測定と電顕観察より査読有り

符徳勝, 谷口博基, 伊藤満, 森茂生

日本物理学会誌 66 巻頁： 270 - 276 2011年

Molecular Beam Deposition of Nanoscale Ionic Liquids in Ultrahigh Vacuum 査読有り

Maruyama Shingo, Takeyama Yoko, Taniguchi Hiroki, Fukumoto Hiroki, Itoh Mitsuru, Kumigashira Hiroshi, Oshima Masaharu, Yamamoto Takakazu, Matsumoto Yuji

ACS NANO 4 巻 ( 10 ) 頁： 5946 - 5952 2010年10月

Dielectric and soft-mode behaviors of AgTaO3 査読有り

Soon Hwee Ping, Taniguchi Hiroki, Itoh Mitsuru

PHYSICAL REVIEW B 81 巻 ( 10 ) 2010年3月

Ferroelectricity in NaNbO3: Revisited 査読有り

Arioka Takahiro, Taniguchi Hiroki, Itoh Mitsuru, Oka Kunihiko, Wang Ruiping, Fu Desheng

FERROELECTRICS 401 巻 ( 1 ) 頁： 51 - 55 2010年

Phonon Dynamics in BiFeO3 Studied by Raman Scattering 査読有り

Shimizu Takao, Era Takuro, Taniguchi Hiroki, Fu Desheng, Taniyama Tomoyasu, Itoh Mitsuru

FERROELECTRICS 403 巻 ( 1 ) 頁： 187 - 190 2010年

多重不均一性をもつPb(Mg1/3Nb2/3) O3リラクサー

符徳勝, 谷口博基, 伊藤満, 腰原伸也, 山本直紀, 森茂夫

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2010 巻 ( 0 ) 頁： 3A20 - 3A20 2010年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

電気分極測定、ラマン分光測定、透過型電子顕微鏡（ＴＥＭ）の観察を通して最も典型的なリラクサー材料であるPb(Mg1/3Nb2/3)O3（ＰＭＮ）を対象にしてリラクサーの挙動を系統的に調べた。その結果、(1)通常ＰＭＮで270K付近に観測された巨大な誘電応答は分極反転に由来することが判明した。(2)PMNがＴ＜Ｔc=225以下で多重ドメイン構造を示す強誘電体であることが分かった。

DOI： 10.14853/pcersj.2010S.0.3A20.0

20pHS-11 PMNリラクサーにおける多重スケール不均一性(20pHS 誘電体(リラクサー),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

符徳勝, 谷口博基, 伊藤満, 腰原伸也, 山本直紀, 森茂生

日本物理学会講演概要集 65.1.4 巻 ( 0 ) 頁： 976 2010年

21aPS-88 リラクサーPb(Mg_<1/3>Nb_<2/3>)O_3の低周波数領域光散乱分光(21aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

是枝聡肇, 高野隆太, 齊官清四郎, 谷口博基, 伊藤満

日本物理学会講演概要集 65.1.4 巻 ( 0 ) 頁： 985 2010年

21aPS-87 Pb(Mg_<1/3>Nb_<2/3>)O_3のラマン散乱(21aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

藤井康裕, 和佐田智彦, 谷口博基, 伊藤満

日本物理学会講演概要集 65.1.4 巻 ( 0 ) 頁： 985 2010年

21aPS-86 PMN及びPMN-PTにおける低振動数フォノンダイナミクス(21aPS 領域10ポスターセッション(誘電体),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

谷口博基, 西田恒仁, 橘信, 伊藤満

日本物理学会講演概要集 65.1.4 巻 ( 0 ) 頁： 984 2010年

22pHS-2 CdTiO_3のソフトモードの第一原理計算(22pHS 誘電体・フォノン(酸化物・第一原理計算),領域10(誘電体,格子欠陥,X線・粒子線,フォノン))

森分博紀, 谷口博基, 伊藤満

日本物理学会講演概要集 65.1.4 巻 ( 0 ) 頁： 998 2010年

25aWY-6 ラマン散乱によるBa_<1-x>Ca_xTiO_3の構造相転移の研究(25aWY 酸化物系,領域10(誘電体格子欠陥,X線・粒子線フォノン))

清水荘雄, 符徳勝, 谷口博基, 谷山智康, 伊藤満

日本物理学会講演概要集 65.2.4 巻 ( 0 ) 頁： 916 2010年

24aPS-136 水素結合型強誘電体単結晶における空間的同位体濃度分布制御(24aPS 領域10ポスターセッション,領域10(誘電体格子欠陥,X線・粒子線フォノン))

長田勝士, 谷口博基, 谷山智康, 伊藤満

日本物理学会講演概要集 65.2.4 巻 ( 0 ) 頁： 903 2010年

24aPS-130 透過型電子顕微鏡法による(Ba_<1-x>Ca_x)TiO_3の微細構造評価(24aPS 領域10ポスターセッション,領域10(誘電体格子欠陥,X線・粒子線フォノン))

小山司, 尾崎友厚, 森茂生, 符徳勝, 清水荘雄, 谷口博基, 伊藤満

日本物理学会講演概要集 65.2.4 巻 ( 0 ) 頁： 902 2010年

24aPS-122 リラクサーPb(Mg_<1/3>Nb_<2/3>)O_3の低周波数領域光散乱分光(II)(24aPS 領域10ポスターセッション,領域10(誘電体格子欠陥,X線・粒子線フォノン))

是枝聡肇, 齊官清四郎, 谷口博基, 伊藤満

日本物理学会講演概要集 65.2.4 巻 ( 0 ) 頁： 900 2010年

23pWY-10 PMNのラマン散乱における偏光依存性(23pWY マルチフェロイック・リラクサー,領域10(誘電体格子欠陥,X線・粒子線フォノン))

藤井康裕, 和佐田智彦, 谷口博基, 伊藤満

日本物理学会講演概要集 65.2.4 巻 ( 0 ) 頁： 891 2010年

Dielectric and Soft-mode Behaviors of AgTaO_3 査読有り

谷口博基

Physical Review B vol.81 2010年

Molecular Beam Deposition of Nanoscale Ionic Liquids in Ultrahigh Vacuum 査読有り

谷口博基

ACS Nano 4 巻頁： 5946 - 5952 2010年

Ferroelectricity in NaNbO_3 : Revisited 査読有り

谷口博基

Ferroelectrics 401 巻頁： 51 - 55 2010年

Dielectric and Soft-mode Behaviors of AgTaO_3 査読有り

谷口博基

Physical Review B 80(10) 頁： 1041051 - 7 2010年

Dielectric and Soft-mode Behaviors of AgTaO_3 査読有り

谷口博基

Physical Review B 81 巻頁： 1041051 - 7 2010年

Phonon dynamics in BiFeO_3 studied by Raman scattering 査読有り

谷口博基, 符徳勝, 谷山智康

Ferroelectrics 403 巻頁： 187 2010年

Ferroelectricity in NaNbO3: Revisited 査読有り

谷口博基, 王瑞平

Ferroelectrics Vol. 401 巻頁： 51 - 55 2010年

Ferroelectricity triggered in the quantum paraelectric AgTaO3 by Li-substitution 査読有り

Soon Hwee Ping, Taniguchi Hiroki, Itoh Mitsuru

APPLIED PHYSICS LETTERS 95 巻 ( 24 ) 2009年12月

Relaxor Pb(Mg1/3Nb2/3)O-3: A Ferroelectric with Multiple Inhomogeneities 査読有り

Fu Desheng, Taniguchi Hiroki, Itoh Mitsuru, Koshihara Shin-ya, Yamamoto N., Mori Shigeo

PHYSICAL REVIEW LETTERS 103 巻 ( 20 ) 頁： 207601 2009年11月

Comprehensive Structural Study of Glassy and Metastable Crystalline BaTi2O5 査読有り

Yu Jianding, Kohara Shinji, Itoh Keiji, Nozawa Shunsuke, Miyoshi Satoru, Arai Yasutomo, Masuno Atsunobu, Taniguchi Hiroki, Itoh Mitsuru, Takata Masaki, Fukunaga Toshiharu, Koshihara Shin-ya, Kuroiwa Yoshihiro, Yoda Shinichi

CHEMISTRY OF MATERIALS 21 巻 ( 2 ) 頁： 259 - 263 2009年1月

Soft-mode Dynamics in the Ferroelectric Phase Transition of Quantum Paraelectric SrTiO3 査読有り

Yagi Toshirou, Takesada Masaki, Taniguchi Hiroki, Itoh Mitsuru

FERROELECTRICS 379 巻 ( 1 PART 2 ) 頁： 168 - 176 2009年

BiFeO3の高温ラマン散乱

清水荘雄, 谷口博基, 谷山智康, 符徳勝, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2009 巻 ( 0 ) 頁： 1PA34 - 1PA34 2009年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

BiFeO3は高い自発分極値や室温において強誘電性と反強磁性を有する物質として近年大きな注目を集め非常に多くの研究がなされている。しかしながら強誘電相転移点が820ºC付近と非常に高温であることとさらに物質自体の不安定性もあり、BiFeO3の相転移挙動についてはいまだによくわかっていない。そこで本研究ではBiFeO3単結晶をflux法によって作成したサンプルについてラマン散乱を行った。サンプルは分極軸に垂直な(110)hex面に切り出したものを用いた。ラマンスペクトルの回転依存性及び偏光依存性を調べることによってA1モードとEモードを分離することができた。

DOI： 10.14853/pcersj.2009F.0.1PA34.0

Tuning the orthorhombic-rhombohedral phase transition temperature in sodium potassium niobate by incorporating barium zirconate 査読有り

Wang Ruiping, Bando Hiroshi, Katsumata Tetsuhiro, Inaguma Yoshiyuki, Taniguchi Hiroki, Itoh Mitsuru

PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 3 巻 ( 5 ) 頁： 142 - 144 2009年

LiNbO3におけるRaman散乱強度の組成依存性

大登正敬, 国原健二, 広瀬隆之, 谷口博基, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2009 巻 ( 0 ) 頁： 166 - 166 2009年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

LiNbO3（Lithium Niobate: LN）は、表面弾性波デバイスおよび非線形光学素子として広く使用されている材料であり、これまで多くの研究がなされている。今回、いくつかのRaman散乱ピーク強度の組成依存性を測定し、LN結晶欠陥との関連を調べた。組成およびMg添加量の異なる４種類のLNについて、バックスキャッター配置でラマン測定を行った。その結果、いくつかの散乱ピークに著しい組成依存性を窺うことができた。これらのピークに対し、いくつかの仮定の下で理論解析を行い、欠陥量の相対比較をおこなった。その結果、それぞれのピークがLNの欠陥（Ndアンチサイト欠陥・Li空孔）に関連していると考えると、上述した組成依存性は欠陥平衡モデルに照らし合わせ矛盾なく説明できる。

DOI： 10.14853/pcersj.2009S.0.166.0

精密共焦点顕微ラマン分光法によるアンチパラレルドメイン構造のイメージング

谷口博基, 大登正敬, 広瀬隆之, 国原健二, 藤井康裕, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2009 巻 ( 0 ) 頁： 1G20 - 1G20 2009年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

独自に開発した精密共焦点顕微分光システムを用いて、LiNbO3単結晶におけるアンチパラレルドメイン構造の観測を行った。従来、アンチパラレルドメインはラマン選択則の等価性の為にラマン分光法では観測不可能と考えられてきた。それに対して本研究では、ドメイン境界に生じる微小な格子歪みを高精度で検出することにより、LiNbO3のアンチパラレルドメインを500nm以下の空間分解能で正確に観測することに成功した。本研究の結果は、非接触・非破壊・非侵襲による革新的なドメインイメージング技術を新たに開拓するものである。さらに、詳細なスペクトル解析によってドメイン境界に生じる格子歪みの原因も明らかにしたので、この結果も合わせて報告する。

DOI： 10.14853/pcersj.2009F.0.1G20.0

27pPSB-11 Pb(Mg_<1/3>Nb_<2/3>)O_3におけるソフトモードダイナミクス(領域10ポスターセッション(誘電体),領域10,誘電体,格子欠陥,X線・粒子線,フォノン物性)

谷口博基, 清水荘雄, 符徳勝, 伊藤満

日本物理学会講演概要集 64.2.4 巻 ( 0 ) 頁： 885 2009年

30pRF-4 ラマン散乱によるペロブスカイト型誘電体酸化物の構造相転移の研究(30pRF 誘電体(ペロブスカイト),領域10(誘電体,格子欠陥,X線・粒子線,フォノン物性))

谷口博基, 清水荘雄, 藤井康裕, 橘信, 符徳勝, 伊藤満

日本物理学会講演概要集 64.1.4 巻 ( 0 ) 頁： 984 2009年

28pRB-2 ホモエピタキシャルSTO18薄膜の構造相転移(28pRB 誘電体(SrTiO_3系),領域10(誘電体,格子欠陥,X線・粒子線,フォノン物性))

藤井康裕, 谷口博基, 伊藤満, 片山正士, 松本祐司

日本物理学会講演概要集 64.1.4 巻 ( 0 ) 頁： 951 2009年

28aXA-1 精密共焦点顕微ラマンイメージング法を用いたLiNbO_3のアンチパラレルドメイン構造の可視化(誘電体の光制御・光応答,新光源・新分光法,領域5,領域10合同,領域5,光物性)

谷口博基, 大登正敬, 広瀬隆之, 国原健二, 藤井康裕, 伊藤満

日本物理学会講演概要集 64.2.4 巻 ( 0 ) 頁： 680 2009年

27pPSB-17 NaNbO_3の誘電測定(領域10ポスターセッション(誘電体),領域10,誘電体,格子欠陥,X線・粒子線,フォノン物性)

有岡孝祐, 谷口博基, 谷山智康, 伊藤満, 符徳勝

日本物理学会講演概要集 64.2.4 巻 ( 0 ) 頁： 887 2009年

27pPSB-14 Ba_<0.767>Ca_<0.233>TiO_3の格子振動ダイナミクス(領域10ポスターセッション(誘電体),領域10,誘電体,格子欠陥,X線・粒子線,フォノン物性)

清水荘雄, 符徳勝, 谷口博基, 谷山智康, 伊藤満

日本物理学会講演概要集 64.2.4 巻 ( 0 ) 頁： 886 2009年

Ferroelectricity Triggered in the Quantum Paraelectric AgTaO_3 by Li-substitution 査読有り

谷口博基

Applied Physics Letters vol.95 2009年

Ferroelectricity Triggered in the Quantum Paraelectric AgTaO_3 by Li-substitution 査読有り

谷口博基

Applied Physics Letters 95(24) 頁： 2429041 - 3 2009年

Soft-mode Dynamics in the Ferroelectric Phase Transition of Quantum Paraelectric SrTiO_3 査読有り

谷口博基

Ferroelectrics 379 頁： 168 - 176 2009年

Tuning the Orthorhombic-Rhombohedral Phase Transition Temperature in Sodium Potassium Niobate by Barium Zirconate 査読有り

谷口博基

Physica Status Solidi-Rapid Research Letters 3(5) 頁： 142 - 144 2009年

Direct observation of the soft mode in the paraelectric phase of PbTiO(3) by confocal micro-Raman scattering 査読有り

Soon Hwee Ping, Taniguchi Hiroki, Fujii Yasuhiro, Itoh Mitsuru, Tachibana Makoto

PHYSICAL REVIEW B 78 巻 ( 17 ) 2008年11月

Reply to Comment on "Origin of Giant Dielectric Response in Nonferroelectric CaCu3Ti4O12: Inhomogeneous Conduction Nature Probed by Atomic Force Microscopy"

Fu Desheng, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru, Koshihara Shin-ya

CHEMISTRY OF MATERIALS 20 巻 ( 19 ) 頁： 6286 - 6287 2008年10月

Ferroelectric phase transition of Cd2 Nb2 O7 studied by Raman scattering 査読有り

Hiroki Taniguchi, Takao Shimizu, Hitoshi Kawaji, Tooru Atake, Mitsuru Itoh, Makoto Tachibana

Physical Review B - Condensed Matter and Materials Physics 77 巻 ( 22 ) 2008年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Cadmium pyroniobate (Cd2 Nb2 O7: CNO) is a recent focus in the ferroelectric materials due to its unusual diffuse-phase transition without any compositional fluctuation, unlike conventional relaxors. In the present study, the critical dynamics of CNO was studied by the confocal micro-Raman scattering. The heavily overdamped soft-mode spectra have been resolved in the ferroelectric phase. The coupled-mode analysis successfully extracted the contribution of the relaxational mode from the overdamped soft mode. The decomposed soft mode clearly shows the Landau-type critical behavior with γ=1. The relaxation was reasonably assigned to the hopping motion of Cd ions from its activation energy of ∼21 meV. The phase transition of CNO, in spite of diffusive characteristics in the dielectric peak, is concluded to be purely driven by the conventional softening of the soft mode, which is heavily overdamped due to the coupling with Cd-hoping mode. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.224104

25pYE-1 パイロクロア型強誘電体Cd_2Nb_2O_7におけるソフトモードの臨界挙動と相転移(誘電体(酸化物系),領域10,誘電体,格子欠陥,X線・粒子線,フォノン物性)

Origin of giant dielectric response in nonferroelectric CaCu3Ti4O12: Inhomogeneous conduction nature probed by atomic force microscopy 査読有り

Fu Desheng, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru, Koshihara Shin-ya

CHEMISTRY OF MATERIALS 20 巻 ( 5 ) 頁： 1694 - 1698 2008年3月

Successive crystallization of ferroelectric-based BaTi2O5 bulk glass studied by Raman scattering 査読有り

Taniguchi Hiroki, Yu Jianding, Arai Yasutomo, Fu Desheng, Yagi Toshirou, Itoh Mitsuru

MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS 148 巻 ( 1-3 ) 頁： 48 - 52 2008年2月

Dynamics of the Ferroelectric Phase Transition in 18O-exchanged SrTiO3 Studied by Raman Scattering 査読有り

Taniguchi Hiroki, Yagi Toshirou, Itoh Mitsuru

FERROELECTRICS 369 巻 ( 1 PART 3 ) 頁： 3 - 9 2008年

谷口博基, 清水荘雄, 橘信, 川路均, 阿竹徹, 伊藤満

日本物理学会講演概要集 63.1.4 巻 ( 0 ) 頁： 944 2008年

Temperature Evolution of the Optical Phonons in Pb(Ni1/3Nb2/3)O-3 Single Crystals Studied by Raman Scattering 査読有り

Kano Jun, Taniguchi Hiroki, Fu Desheng, Itoh Mitsuru, Kojima Seiji

FERROELECTRICS 367 巻 ( 1 PART 1 ) 頁： 67 - 72 2008年

Piezoelectric properties of lithium modified silver niobate perovskite single crystals 査読有り

Fu Desheng, Endo Makoto, Taniguchi Hiroki, Taniyama Tomoyasu, Koshihara Shin-ya, Itoh Mitsuru

APPLIED PHYSICS LETTERS 92 巻 ( 17 ) 2008年

Ferroelectricity in Perovskite-Type Oxides 査読有り

Itoh Mitsuru, Taniguchi Hiroki

FERROELECTRICS 369 巻 ( 1 PART 3 ) 頁： 127 - 132 2008年

Ferroelectric phase transition of <math display="inline"> <mrow> <msub> <mrow> <mtext>Cd</mtext> </mrow> <mn>2</mn> </msub> <msub> <mrow> <mtext>Nb</mtext> </ 査読有り

Taniguchi Hiroki, Shimizu Takao, Kawaji Hitoshi, Atake Tooru, Itoh Mitsuru, Tachibana Makoto

Physical Review B 77 巻 ( 22 ) 頁： 224104 2008年

CdTiO3のソフトモードの第一原理計算

森分博紀, 平山司, 田中功, 谷口博基, 伊藤満, 単躍進

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2008 巻 ( 0 ) 頁： 184 - 184 2008年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

ペロブスカイト型構造を有するCdTiO3は室温ではTiO6八面体が回転したPnma構造をとり，約85Kにおいて強誘電体に転移することが報告されているが，その強誘電相の構造などはこれまで詳細な解析はなされていなかった．本研究では，第一原理計算によるフォノン分散の計算を行い，Pnma相におけるソフトモードの存在，また，そのソフトモードから導かれる低対称性相について検討を行った．

DOI： 10.14853/pcersj.2008F.0.184.0

21aVE-9 CdTiO_3の強誘電体相転移に関する第一原理計算(21aVE 誘電体(第一原理計算),領域10(誘電体,格子欠陥,X線・粒子線,フォノン物性))

森分博紀, 平山司, 田中功, 谷口博基, 伊藤満, 単躍進

日本物理学会講演概要集 63.2.4 巻 ( 0 ) 頁： 870 2008年

22aVE-7 PbTiO_3におけるセントラルピークの起源としての新奇な低エネルギー励起の発見(22aVE 誘電体(フォノンダイナミクス),領域10(誘電体,格子欠陥,X線・粒子線,フォノン物性))

谷口博基, 橘信, 伊藤満

日本物理学会講演概要集 63.2.4 巻 ( 0 ) 頁： 884 2008年

Comprehensive Structural Study of Glassy and Metastable Crystalline BaTiO 査読有り

谷口博基

Chemistry of Materials 21 頁： 259 - 263 2008年

Ferroelectricity in Perovskite-Type Oxides 査読有り

谷口博基

Ferroelectrics 369 頁： 127 - 132 2008年

Ferroelectric Phase Transition of Cd_2Nb_2O_7 Studied by Raman Scattering 査読有り

谷口博基

Physical Review B vol.77 2008年

Dynamics of the Ferroelectric Phase Transition in ^<18>O-exchanged SrTiO_3 Studied by Raman Scattering 査読有り

谷口博基

Ferroelectrics 369 頁： 3 - 9 2008年

Direct Observation of the Soft Mode in the Paraelectric Phase of PbTiO_3 by Confocal Micro-Raman Scattering 査読有り

谷口博基

Physical Review B vol.78 2008年

Direct Observation of the Soft Mode in the Paraelectric Phase of PbTiO_3 by Confocal Micro-Raman Scattering 査読有り

谷口博基

Physical Review B 78 2008年

Origin of Giant Dielectric Response in Nonferroelectric CaCu_3Ti_4O_12 : Inhomogeneous Conduction Nature Probed by Atomic Force Microscopy 査読有り

谷口博基, 谷山智康

Chemistry of Materials vol.20 頁： 1694 - 1698 2008年

Temperature Evolution of the Optical Phonons in Pb(Ni_<1/3>Nb_<2/3>)O_3 Single Crystals Studied by Raman Scattering 査読有り

谷口博基

Ferroelectrics 369 頁： 67 - 72 2008年

Successive Crystallization of Ferroelectric-based BaTi_2O_5 Bulk Glass Studied by Raman Scattering 査読有り

谷口博基

Materials Science and Engineering B 148 頁： 48 - 52 2008年

Reply to Comment on “Origin of Giant Dielectric Response in Nonferroelectric CaCu_3Ti_4O_<12> : Inhomogeneous Conduction Nature Probed by Atomic Force Microscopy" 査読有り

谷口博基, 谷山智康

Chemistry of Materials" 20 頁： 6286 - 6287 2008年

Piezoelectric Properties of Lithium Modified Silver Niobate Perovskite Single Crystals 査読有り

谷口博基, 谷山智康

Applied Physics Letters vol.92 2008年

Critical soft-mode dynamics and unusual anticrossing in CdTi O3 studied by Raman scattering 査読有り

Hiroki Taniguchi, Yue Jin Shan, Hajime Mori, Mitsuru Itoh

Physical Review B - Condensed Matter and Materials Physics 76 巻 ( 21 ) 2007年12月

記述言語：英語掲載種別：研究論文（学術雑誌）

The ferroelectric phase transition and the critical soft-mode behavior of CdTi O3 were investigated by confocal micro-Raman scattering. The soft mode softens toward zero frequency at Tc with the underdamped vibrational state, indicating ideal displacive-type ferroelectric phase transition. The continuous development of the spectra of ferroelectric modes clarified the second-order phase transition of CdTi O3. The soft mode undergoes an unusual splitting during the softening, which is reasonably explained by anticrossing between the soft mode and the different symmetry mode due to the local symmetry breakdown into the triclinic one. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.76.212103

Critical soft-mode dynamics and unusual anticrossing in CdTiO3 studied by Raman scattering 査読有り

Hiroki Taniguchi, Yue Jin Shan, Hajime Mori, Mitsuru Itoh

PHYSICAL REVIEW B 76 巻 ( 21 ) 2007年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The ferroelectric phase transition and the critical soft-mode behavior of CdTiO3 were investigated by confocal micro-Raman scattering. The soft mode softens toward zero frequency at T-c with the underdamped vibrational state, indicating ideal displacive-type ferroelectric phase transition. The continuous development of the spectra of ferroelectric modes clarified the second-order phase transition of CdTiO3. The soft mode undergoes an unusual splitting during the softening, which is reasonably explained by anticrossing between the soft mode and the different symmetry mode due to the local symmetry breakdown into the triclinic one.

DOI： 10.1103/PhysRevB.76.212103

Light scattering study of the phase transition in quantum paraelectric strontium titanate

Yagi T., Takesada M., Taniguchi H., Itoh M.

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 51 巻 ( 2 ) 頁： 798-803 2007年8月

Light scattering study of the phase transition in quantum paraelectric strontium titanate 査読有り

T. Yagi, M. Takesada, H. Taniguchi, M. Itoh

Journal of the Korean Physical Society 51 巻 ( 2 PART I ) 頁： 798 - 803 2007年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：KOREAN PHYSICAL SOC

New features of the ferroelectric phase transition are found by using light scattering studies on quantum paraelectric SrTi16O3 (STO16) and its oxygen-isotope exchanged compound SrTi18O3 (STO18). The ferroelectric Eu mode observed by using high-resolution spectroscopy with interferometry shows a perfect softening at the phase transition point of the ferroelectric STO18-95, where 95 % of the oxygen atoms are replaced by the oxygen isotope 18O. The phase transition is concluded to be an ideal displacive-type transition accompanied with the complete freezing of the Slater-type polar mode. The role of the substituted 18O atoms is elucidated in more detail by using low-frequency Raman scattering below 1 K with a triple monochromator. The dynamical inhomogeneity enhanced by the inhomogeneous distribution of 18O atoms plays an essential role in quantum paraelectric STO18 where the concentration of 18O is less than the critical value of 33 %. Both the decrease in the frequency of the polar modes as a mass effect and the enhancement of the dynamical inhomogeneity take place cooperatively in the quantum paraelectric-ferroelectric phase transition in STO18.

22pTE-3 CdTiO_3における変位型強誘電相転移とソフトモード(誘電体(酸化物系),領域10,誘電体,格子欠陥,X線・粒子線,フォノン物性)

Ideal soft mode-type quantum phase transition and phase coexistence at quantum critical point in O-18-exchanged SrTiO3 査読有り

Taniguchi Hiroki, Itoh Mitsuru, Yagi Toshirou

PHYSICAL REVIEW LETTERS 99 巻 ( 1 ) 頁： 017602 2007年7月

Recent topics on the light scattering study of ferroelectrics 査読有り

Yagi Toshirou, Takesada Masaki, Taniguchi Hiroki, Itoh Mitsuru

FERROELECTRICS 355 巻 ( 1 PART 1 ) 頁： 3 - 12 2007年

谷口博基, 単躍進, 森基, 伊藤満

日本物理学会講演概要集 62.2.4 巻 ( 0 ) 頁： 996 2007年

Conductive Boundary Layer in CaCu3Ti4O12 with Giant-Dielectric-Response 査読有り

Fu Desheng, Arima Yosuke, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru, Yu Jianding, Koshihara Shin-Ya

FERROELECTRICS 347 巻頁： 140 - 144 2007年

AgNbO3: A lead-free material with large polarization and electromechanical response 査読有り

Fu Desheng, Endo Makoto, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru

APPLIED PHYSICS LETTERS 90 巻 ( 25 ) 2007年

銀系酸化物における巨大電気分極

符徳勝, 遠藤誠, 谷口博基, 谷山智康, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2007 巻 ( 0 ) 頁： 503 - 503 2007年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

Pb系ABO3型酸化物が優れた圧電性や強誘電性を有するのはA-site元素である鉛と酸素の強い結合性によって生じる原子変位に深く関係すると報告されている。それは非鉛系新規材料の探索に良い指針を与えてくれる。われわれはAg系酸化物に52uC/cm2以上極めて大きな分極が存在することを発見した。その巨大な分極がA-siteのAgとOの結合に由来すると提案している。その発見は新規強誘電体の開発に新たな道を開くことを強く期待している。

DOI： 10.14853/pcersj.2007F.0.503.0

Ferroelectricity of SrTiO3 Induced by Oxygen Isotope Exchange

谷口博基

Structure and Bonding 124 頁： 89 - 118 2007年

その場観測ラマン散乱を用いた強誘電体ガラスの結晶化過程の研究

谷口博基

ニューガラス 84 頁： 57 2007年

Ferroelectricity of SrTiO3 induced by oxygen isotope exchange 査読有り

Itoh Mitsuru, Taniguchi Hiroki

FERRO- AND ANTIFERROELECTRICITY: ORDER/DISORDER VERSUS DISPLACIVE 124 巻頁： 89 - 118 2006年12月

Precursory softening of polar mode in isotope-exchanged paraelectric strontium titanate studied by Raman scattering 査読有り

Taniguchi H., Takesada M., Itoh M., Yagi T.

FERROELECTRICS 337 巻頁： 131 - 138 2006年8月

Fabrication of BaTi2O5 glass-ceramics with unusual dielectric properties during crystallization

Yu JD, Arai Y, Masaki T, Ishikawa T, Yoda S, Kohara S, Taniguchi H, Itoh M, Kuroiwa Y

CHEMISTRY OF MATERIALS 18 巻 ( 8 ) 頁： 2169 - 2173 2006年4月

Crystal growth of 50mg-class single crystals of beta '-(BEDT-TTF)(2)ICl2 and crystal evaluation

Taniguchi H., Sato R., Satoh K., Kawamoto A., Okamoto H., Kobayasi T., Mizuno K.

JOURNAL OF LOW TEMPERATURE PHYSICS 142 巻 ( 3-4 ) 頁： 437 - 440 2006年2月

Raman scattering study of superionic conductor lithium tetraborate Li2B4O7 査読有り

Dekola T, Yagi T, Taniguchi H, Takesada M, Sekine L

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 巻 ( 1 A ) 頁： 152 - 154 2006年1月

In Situ Raman Scattering Study on Successive Crystallization of Bulk BaTi2O5 Glass

Taniguchi Hiroki, Yu Jianding, Arai Yasutomo, Yagi Toshirou, Fu Desheng, Itoh Mitsuru

日露/CIS/バルチック強誘電体シンポジウム講演概要集 2006 巻 ( 0 ) 頁： 42 - 42 2006年

ラマン散乱を用いたBaTi2O5ガラスの結晶化過程のその場観察

谷口博基, 余野建定, 荒井康智, 八木駿郎, 符徳勝, 伊藤満

日本セラミックス協会　年会・秋季シンポジウム講演予稿集 2006 巻 ( 0 ) 頁： 19 - 19 2006年

掲載種別：研究論文（学術雑誌）出版者・発行元：公益社団法人日本セラミックス協会

無容器法によって作製されたBaTi2O5ガラスは、強誘電体を基にしてガラス形成物質の添加無しに作られた初めてのバルクガラスであり、新ガラス材料として極めて多くの注目を集めている。この物質は結晶化過程において107にも及ぶ巨大な誘電異常を示すがその起源は明らかになっておらず、結晶化過程の解明が強く望まれている。本研究ではラマン散乱を用いてBaTi2O5ガラス結晶化過程のその場観察を行なった。その結果、α相とβ相の２つの準安定ナノ結晶相の生成を伴った段階的な結晶化過程を明らかにした。さらに巨大な誘電異常がα相に起因することを解明した。

DOI： 10.14853/pcersj.2006F.0.19.0

Soft mode dynamics in O-18-exchanged SrTiO3 as inhomogeneous system 査読有り

Hiroki Taniguchi, Mitsuru Itoh, Masaki Takesada, Toshirou Yagi

TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN, VOL 31, NO 1 31 巻 ( 1 ) 頁： 97 - 100 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：ELSEVIER SCIENCE BV

Ferroelectric phase transition of quantum paraelectric SrTiO3 is induced by an exchange of O-16 for its isotope O-18 in a low temperature region. The dynamics of ferroelectric soft mode in weakly O-18-exchanged strontium titanate is studied by Raman scattering. A nominally Raman-inactive soft mode is observed in the paraelectric phase of SrTi((O0.32O0.68)-O-18-O-16)(3) due to the local symmetry-breaking. The observed soft mode spectrum shows the temperature dependence strongly affected by the inhomogeneity of the system. The soft mode nonuniformly freezes to induce the local ferroelectric order before the onset of ferroelectric phase. The dynamical inhomogeneity is concluded to play an essential role in the dielectric response of O-18-exchanged strontium titanate.

Ferroelectricity of SrTi18O3: Paradox in the Phase Transition Mechanism

Itoh Mitsuru, Taniguchi Hiroki

日露/CIS/バルチック強誘電体シンポジウム講演概要集 2006 巻 ( 0 ) 頁： 3 - 3 2006年

Conductive Boundary Layer in CaCu3Ti4O12 with Giant-Dielectric-Response

Fu Desheng, Arima Yosuke, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsru, Yu Jianding, Koshihara Shin-ya

日露/CIS/バルチック強誘電体シンポジウム講演概要集 2006 巻 ( 0 ) 頁： 80 - 80 2006年

Isotope effect on the soft-mode dynamics of SrTiO3 studied by Raman scattering 査読有り

Taniguchi H, Yagi T, Takesada M, Itoh M

PHYSICAL REVIEW B 72 巻 ( 6 ) 2005年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Review B - Condensed Matter and Materials Physics

The oxygen isotope effect on the soft-mode dynamics in quantum paraelectric SrTi (Ox18 O 1-x 16) 3 [STO18- x] is investigated by Raman scattering in terms of local symmetry breaking in the paraelectric phase. The exchange rates x of the O18 atoms are 0.23 [STO18-23] and 0.32 [STO18-32], which are less than the critical value xc (=0.33). In STO18-32, whose exchange rate is just below xc, the soft Eu mode shows hardening behavior in a low-temperature region indicating the onset of local ferroelectric order. On the other hand, the soft Eu mode in STO18-23 does not show any hardening behavior until 0 K. The enhancement of the inhomogeneity in the crystal by the exchange of O18 is concluded to play an essential role in the soft-mode dynamics of the quantum paraelectric and ferroelectric STO18- x. The relation between the soft-mode dynamics and quantum fluctuation is discussed. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.064111

19pYM-11 Raman Scattering Study of Superionic Conductor Lithium Tetraborate Li_2B_4O_7. Part II

Growth of ferroelectric micro-regions in SrTiO3 and SrTi((O0.23O0.77)-O-18-O-16)(3) studied by Raman scattering 査読有り

Taniguchi H, Yagi T, Takesada M, Itoh M

JOURNAL OF THE KOREAN PHYSICAL SOCIETY 46 巻 ( 1 ) 頁： 195 - 197 2005年1月

Dekola Tatiana, Yagi Toshirou, Taniguchi Hiroki, Takesada Masaki, Sekine Ichiro

日本物理学会講演概要集 60.2.4 巻 ( 0 ) 頁： 803 2005年

24aYR-7 Low-frequency modes in Li_2B_4O_7 crystals studied by Raman scattering

Dekola Tatiana, Taniguchi Hiroki, Takesada Masaki, Sekine Ichiro, Yagi Toshirou

日本物理学会講演概要集 60.1.4 巻 ( 0 ) 頁： 890 2005年

25pYR-2 量子常誘電性STO18における局所対称性の前駆的低下とソフトモード(誘電体,領域10(誘電体, 格子欠陥, X線・粒子線, フォノン物性))

谷口博基, 武貞正樹, 伊藤満, 八木駿郎

日本物理学会講演概要集 60.1.4 巻 ( 0 ) 頁： 913 2005年

Growth of Ferroelectric Micro-regions in SrTiO_3 and SrTi(^<18>O_<0.23>^<16>O_<0.77>)_3 Studied by Raman Scattering

谷口博基

Journal of the Korean Physical Society Vol.46 頁： 195 - 197 2005年

Effect of Oxygen Isotope Exchange on Ferroelectric Microregion in SrTiO3Studied by Raman Scattering

Taniguchi Hiroki, Takesada Masaki, Itoh Mitsuru, Yagi Toshirou

Journal of the Physical Society of Japan 73 巻 ( 12 ) 頁： 3262 - 3265 2004年12月

Effect of oxygen isotope exchange on ferroelectric microregion in SrTiO3 studied by Raman scattering 査読有り

Taniguchi H, Takesada M, Itoh M, Yagi T

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 巻 ( 12 ) 頁： 3262 - 3265 2004年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

The ferroelectric microregion (FMR) in quantum paraelectric SrTiO3 is studied by Raman scattering using an optical cryostat with a 3He refrigerator. By the partial exchange of the oxygen atom for its isotope 18O, broad FMR spectra change drastically to underdamped Lorentzian-type spectra with decreasing temperature below 10 K. The peak is assigned to the ferroelectric soft Eu mode. The intense and sharp spectra of the Eu mode, which are nominally Raman inactive, indicate that the symmetry is lowered to a non-centrosymmetric symmetry in FMR. Furthermore, the softening characteristic of the soft Eu mode in a low-temperature region implies that the symmetry is not necessarily ferroelectric. The local symmetry breaking is enhanced by the substitution of the isotope 18O.

DOI： 10.1143/JPSJ.73.3262

Neutron Diffraction Study of Crystal Structures of Deuterated Glycinium Phosphite in Paraelectric and Ferroelectric Phases

Machida Mitsuo, Uchida Hiroyuki, Ishibashi Toku, TANIGUCHI Hiroki, KOMUKAE Masaru, OSAKA Toshio, KOYANO Nobumitsu

Journal of the Physical Society of Japan 73 巻 ( 1 ) 頁： 107 - 115 2004年1月

掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

Crystal structure of deuterated glycinium phosphite was studied in the paraelectric (P) phase at 348 K and in the ferroelectric (F) phase at 223 K by means of the single crystal neutron diffraction. Deuteration rate is estimated to be 0.939 by the least-squares refinement. In the P phase, quasi-one-dimensional hydrogen bond chains are built by mutually linking the DPO^<2->_3 anions through two different types of hydrogen bonds with the bond angles of 179.2 and 171.6°. Two independent deuterons within the hydrogen bonds forming the chains are disordered over two sites separated by 0.545 and 0.539 Å. In the F phase, they order at a position nearly equal to one of two sites related by the disorder in the P phase. With the ordering of the deuterons, the P-O bonds with covalently bonded deuteron elongate, and those without covalently bonded deuteron reduce their lengths to some extent from the values determined in the P phase. Two oxygens involved in the hydrogen bond with the bond angle 179.2° exhibits especially large displacements in the F phase. This suggests strongly an importance of this hydrogen bond in the polarization appearance and in the ferroelectric transition. Comparison with results of non-deuterated salt indicates that only the hydrogen bonds forming the chains show significant isotope shift. In particular, the hydrogen bond with the bond angle 179.2° exhibits the most pronounced shift on the angle parameter defined by the angle between the line connecting two sites of disordered proton or deuteron and the line connecting two oxygens involved in the hydrogen bond.

Neutron Diffraction Study of Crystal Structures of Deuterated Glycinium Phosphite in Paraelectric and Ferroelectric Phases

Machida Mitsuo, Uchida Hiroyuki, Ishibashi Toku, Taniguchi Hiroki, Komukae Masaru, Osaka Toshio, Koyano Nobumitsu

Journal of the Physical Society of Japan 73 巻 ( 1 ) 頁： 107 - 115 2004年1月

Neutron diffraction study of crystal structures of deuterated glycinium phosphite in paraelectric and ferroelectric phases 査読有り

Machida M, Uchida H, Ishibashi T, Taniguchi H, Komukae M, Osaka T, Koyano N

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 73 巻 ( 1 ) 頁： 107 - 115 2004年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

Crystal structure of deuterated glycinium phosphite was studied in the paraelectric (P) phase at 348 K and in the ferroelectric (F) phase at 223 K by means of the single crystal neutron diffraction. Deuteration rate is estimated to be 0.939 by the least-squares refinement. In the P phase, quasi-one-dimensional hydrogen bond chains are built by mutually linking the DPO32− anions through two different types of hydrogen bonds with the bond angles of 179.2 and 171.6°. Two independent deuterons within the hydrogen bonds forming the chains are disordered over two sites separated by 0.545 and 0.539 Å. In the F phase, they order at a position nearly equal to one of two sites related by the disorder in the P phase. With the ordering of the deuterons, the P–O bonds with covalently bonded deuteron elongate, and those without covalently bonded deuteron reduce their lengths to some extent from the values determined in the P phase. Two oxygens involved in the hydrogen bond with the bond angle 179.2° exhibits especially large displacements in the F phase. This suggests strongly an importance of this hydrogen bond in the polarization appearance and in the ferroelectric transition. Comparison with results of non-deuterated salt indicates that only the hydrogen bonds forming the chains show significant isotope shift. In particular, the hydrogen bond with the bond angle 179.2° exhibits the most pronounced shift on the angle parameter defined by the angle between the line connecting two sites of disordered proton or deuteron and the line connecting two oxygens involved in the hydrogen bond.

DOI： 10.1143/JPSJ.73.107

13pTL-9 SrTiO_3 における強誘電性マイクロ領域の同位元素置換効果(誘電体, 領域 10)

谷口博基, 武貞正樹, 伊藤満, 八木駿郎

日本物理学会講演概要集 59.2.4 巻 ( 0 ) 頁： 867 2004年

Effect of Oxygen Isotope Exchange on Ferroelectric Microregion in SrTiO_3 Studied by Raman Scattering

谷口博基

Journal of the Physical Society of Japan Vol.73 頁： 3262 - 3265 2004年

Neutron Diffraction Study of Crystal Structures of Glycinium Phosphite H3NCH2COOH·H2PO3in Paraelectric and Ferroelectric Phases

Taniguchi Hiroki, Machida Mitsuo, Koyano Nobumitsu

Journal of the Physical Society of Japan 72 巻 ( 5 ) 頁： 1111-1117 2003年5月

Neutron diffraction study of crystal structures of glycinium phosphite H3NCH2COOH center dot H2PO3 in paraelectric and ferroelectric phases 査読有り

Taniguchi H, Machida M, Koyano N

Ｊｏｕｒｎａｌ　ｏｆ　ｔｈｅ　Ｐｈｙｓｉｃａｌ　Ｓｏｃｉｅｔｙ　ｏｆ　Ｊａｐａｎ 72 巻 ( 5 ) 頁： 1111 - 1117 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：一般社団法人日本物理学会

Crystal structure of H3NCH2COOH·H2PO3 was studied in the paraelectric phase (P phase) at 298 K and in the ferroelectric phase (F phase) at 170 K by means of the single crystal neutron diffraction. Two independent protons in the hydrogen bonds forming the H(HPO3)− chains are disordered over two sites with the separations of 0.486(3) and 0.474(5) Å in the P phase. In the F phase, they are ordered at a position nearly equal to one of two sites related by the disorder. With the proton order, lengths of the P–O bonds with the oxygens involved in the hydrogen bonds forming the chain deviate from their values determined in the P phase. A possible mechanism for the appearance of the spontaneous polarization is discussed in connection with the deformation of the HPO32− anions in the F phase.

DOI： 10.1143/JPSJ.72.1111