研究者詳細 - 谷口　博基

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

PubMed

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

PubMed

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