研究者詳細 - 谷口　博基

論文 - 谷口　博基

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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

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Scopus

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

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

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

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Scopus

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

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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

Scopus

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

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Scopus

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

Web of Science

Scopus

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

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Scopus

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

Web of Science

Scopus

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