研究者詳細 - 谷口　博基

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

PubMed

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

PubMed

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