Faculty Profiles - TANIGUCHI Hiroki

Papers - TANIGUCHI Hiroki

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Fractal Dynamics in Relaxor Ferroelectrics Studied by Broad-Band Light Scattering Spectroscopy

KOREEDA Akitoshi, FUJII Yasuhiro, TANIGUCHI Hiroki

Nihon Kessho Gakkaishi Vol. 57 ( 4 ) page： 219-225 2015

Language：English Publishing type：Research paper (scientific journal)

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

Raman Tensor Analysis by Angle-Resolved Polarized Spectroscopy

FUJII Yasuhiro, KOREEDA Akitoshi, SHIMIZU Takao, TANIGUCHI Hiroki

Nihon Kessho Gakkaishi Vol. 57 ( 5 ) page： 285-290 2015

Language：English Publishing type：Research paper (scientific journal)

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 Reviewed

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

JOURNAL OF MATERIALS CHEMISTRY C Vol. 3 ( 40 ) page： 10430 - 10435 2015

Language：English Publishing type：Research paper (scientific journal) Publisher：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

Web of Science

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

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

Journal of Materials Chemistry C Vol. 3 ( 40 ) page： 10430 - 10435 2015

Publishing type：Research paper (scientific journal)

© 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

Scopus

21pCJ-2 Mechanism of Ferroelectricity in Perovskite-type Oxides and Prospect for the Development of New Ferroelectric Oxides

Taniguchi Hiroki

Meeting Abstracts of the Physical Society of Japan Vol. 70 ( 0 ) page： 2698 - 2699 2015

21aCH-3 Broad-band Light-scattering Study on PMN-PT III

Ogawa T., Sakai H., Katayama D., Fujii Y., Koreeda A., Taniguchi H.

Meeting Abstracts of the Physical Society of Japan Vol. 70 page： 2664 - 2664 2015

22pCH-8 Ferroelectricity in Aluminate Zeolite Ca_8[Al_<12>O_<24>](WO_4)_2[CAW]

Maeda Y., Moriyoshi C., Kuroiwa Y., Hirose S., Okazaki R., Terasaki I., Taniguchi H.

Meeting Abstracts of the Physical Society of Japan Vol. 70 page： 2738 - 2738 2015

21pBC-10 Correlation between magnetic and transport properties in CaRu_<1-x>Sc_xO_3

Yamamoto T. D., Okazaki R., Taniguchi H., Terasaki I.

Meeting Abstracts of the Physical Society of Japan Vol. 70 page： 2024 - 2024 2015

21aCH-4 Raman spectroscopic study on PMN-PT single crystals

Fujii Y., Ogawa T., Sakai H., Koreeda A., Taniguchi H.

Meeting Abstracts of the Physical Society of Japan Vol. 70 page： 2665 - 2665 2015

Photo-transport properties of Pb<inf>2</inf>CrO<inf>5</inf> single crystals Reviewed

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

Journal of Applied Physics Vol. 116 ( 19 ) page： 193706 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

© 2014 AIP Publishing LLC. We report photo-thermoelectric transport phenomena in Pb2CrO5 single crystals. Without illumination, this material exhibits an insulating behavior characterized by an activation-type temperature variation of the electrical conductivity. The Seebeck coefficient contrastingly shows a crossover from high-temperature insulating to low-temperature metallic behavior, which is attributed to degenerate carriers in a donor level. We have found that under illumination, both the conductivity and the Seebeck coefficient increase in magnitude with increasing photon flux density in the degenerate-conduction regime. This result is difficult to understand within a simple photo-doping effect, which usually leads to a decrease in the Seebeck coefficient under illumination. The observed phenomenon is discussed in terms of a two-carrier contribution to the transport properties.

DOI： 10.1063/1.4902248

Web of Science

Scopus

CiNii Research

Structural changes and microstructures in stuffed tridymite-type compounds Ba<inf>1-x</inf>Sr<inf>x</inf>Al<inf>2</inf>O<inf>4</inf> Reviewed

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

Japanese Journal of Applied Physics Vol. 53 ( 9 ) 2014.10

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

© 2014 The Japan Society of Applied Physics. Crystal structures and microstructures in Ba1-xSrxAl2O4solid solutions between the end members of BaAl2O4 and SrAl2O4 have been carefully investigated by powder X-ray diffraction, electron diffraction and transmission electron microscopy (TEM) imaging experiments. With the help of fast Fourier transform (FFT) calculation, high-resolution TEM images suggested that diffuse streaks along three equivalent o110p directions in the (001) plane, which appear in the P63structure of Ba1-xSrxAl2O4for x = 0.4, originate from the large structural fluctuation of the AlO4 tetrahedral network. On the other hand, the monoclinic P21structure in Ba1-xSrxAl2O4with x = 0.7 was found to consist of a modulated structure with q - 0; 1=2; 0. The present experimental results reveal that a structural phase boundary exists at approximately x = 0.6 between the P63 structure with a large structural fluctuation and a monoclinic P21phase with the single-q modulated structure.

DOI： 10.7567/JJAP.53.09PB01

Web of Science

Scopus

Structural phase transition and microstructures in stuffed tridymite-type compounds; Ba(Al, Fe)<inf>2</inf>O<inf>4</inf>

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

Ferroelectrics Vol. 464 ( 1 ) page： 116 - 121 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

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

Web of Science

Scopus

Pseudogap observed in the charge transport in the thermoelectric oxide Ca<inf>3-x</inf>Bi<inf>x</inf>Co<inf>4</inf>O<inf>9</inf> single crystals Reviewed

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

Journal of the Physical Society of Japan Vol. 83 ( 5 ) page： 054710 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

© 2014 The Physical Society of Japan. We have prepared a set of single crystals of Ca3-xBixCo4O9 using a KCl/K2CO3 flux technique, and have measured the resistivity and Seebeck coefficient along the in-plane direction at low temperatures. In a single crystal of Ca2.8Bi0.2Co4O9, the resistivity reaches a value as low as 1mΩ cm at 70 K, where the mean free path is longer than the de Broglie length of the carrier. This clearly indicates that the non-metallic resistivity in Ca2.8Bi0.2Co4O9 is not due to carrier localization, which is seriously incompatible with a widely-accepted picture of this oxide. We have found that the low-temperature conductivity linearly changes with temperature below 20 K, and the observed temperature dependence is milder than that of the variable range hopping. We propose that this temperature dependence partly comes from pseudogap opening, i.e., anomalous suppression in the density of states.

DOI： 10.7566/JPSJ.83.054710

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

Journal of the Physical Society of Japan Vol. 83 ( 5 ) page： 54710 - 54710 2014.5

Electrical oscillation in SmS induced by a constant external voltage Reviewed

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

Physical Review B - Condensed Matter and Materials Physics Vol. 89 ( 19 ) 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We have observed a persistent voltage oscillation induced by constant external electric fields in the nonmagnetic narrow-gap semiconductor SmS. This oscillation appears with a large nonlinear conduction in a relatively low electric field of a few kV/cm. We find that the oscillation frequency clearly changes on addition of an external capacitor parallel to the sample, indicating that the oscillation does not arise from the Joule heating effect. This oscillation is analyzed in terms of a carrier charging-discharging model, which is associated with an electric-field-induced insulator-to-metal transition as proposed in the oxide insulator VO2. This model reasonably explains the observed oscillation phenomenon, implying the existence of a possible instability toward a conductive state driven by the electric field. © 2014 American Physical Society.

DOI： 10.1103/PhysRevB.89.195103

Web of Science

Scopus

Raman tensor analysis of crystalline lead titanate by quantitative polarized spectroscopy Reviewed

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

Ferroelectrics Vol. 462 ( 1 ) page： 8 - 13 2014.4

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

Recently, the mode splitting of B1+E in PbTiO 3-related heterostructures has been attracted wide range of attention because it is considered to represent intrinsic stress in the materials. However, the spectral behaviour of B1+E mods had remained unclear even in the bulk crystal, i.e., they had been often designated as "silent," even though they should be Raman active. This seems because they does not exhibit a significant mode splitting in the bulk crystal. This work employed an angle-resolved quantitative polarized spectroscopy to clarify the unclarity. The precise measurements revealed that the both two modes are ordinary Raman active modes with a minute energy difference. Copyright © 2014 Taylor & Francis Group, LLC.

DOI： 10.1080/00150193.2014.890470

Web of Science

Scopus

Hierarchical dielectric orders in layered ferroelectrics Bi2SiO5 Reviewed

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

IUCrJ Vol. 1 ( Pt 3 ) page： 160 - 164 2014.4

Language：English Publishing type：Research paper (scientific journal) Publisher：INT UNION CRYSTALLOGRAPHY

© © John C.H. Spence 2014. Electric dipole engineering is now an emerging technology for high electron-mobility transistors, ferroelectric random access memory and multiferroic devices etc. Although various studies to provide insight into dipole moment behaviour, such as phase transition, order and disorder states, have been reported, macroscopic spontaneous polarization has been mainly discussed so far. Here, visualization of the electric dipole arrangement in layered ferroelectrics Bi2SiO5 by means of combined analysis of maximum entropy charge density and electrostatic potential distribution analysis based on synchrotron radiation X-ray powder diffraction data is reported. It was found that the hierarchical dipole orders, the weak-ferroelectric and ferroelectric configurations, were observed in the Bi2O2 and the SiO3 layers, respectively, and the ferrielectric configuration was realised by the interlayer interaction. This discovery provides a new method to visualize the local polarization in ferroelectric materials.

DOI： 10.1107/S2052252514008008

Web of Science

Scopus

PubMed

Photo-induced change of dielectric response in BaCoSiO<inf>4</inf> stuffed tridymite Reviewed

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

Journal of Applied Physics Vol. 115 ( 16 ) 2014.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The photodielectric effect is demonstrated in Mott-insulator BaCoSiO 4 with a stuffed-tridymite-type structure under irradiation of visible light at 365 nm. The real part of dielectric permittivity is enhanced by ∼300% with little increase of tan δ in a low-frequency region. Results of diffuse reflectance spectroscopy, first-principles calculations and dielectric measurements suggest that the photodielectric effect stems from a response of photo-excited electrons in an unoccupied upper-Hubbard band for 3d-orbitals of cobalt, which have significantly small mobility due to the unique configuration of Co ions in the stuffed-tridymite-type structure. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4872032

Web of Science

Scopus

Growth and characterization of Cu<inf>2</inf>ZnSn(S<inf>x</inf>Se <inf>1-x</inf>)<inf>4</inf> alloys grown by the melting method Reviewed

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

Journal of Crystal Growth Vol. 386 page： 204 - 207 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

I2-II-IV-VI4 quaternary Cu2ZnSn(S xSe1-x)4 (CZTSSe) alloys were successfully grown by the melting growth method. The powder X-ray diffraction (XRD) pattern of the CZTSSe alloys showed preferred orientations of (112), (220) and (312) planes, confirming the Kesterite structure. In Raman spectra, the A1 mode peaks expected for CZTS and CZTSe were observed in all samples, and no secondary phases were observed. The CZTSSe alloys in this study were slightly Cu-poor, Zn-rich and VI-rich, similar to compositions of polycrystalline thin-film materials that have achieved high photovoltaic conversion efficiencies. Single phase and homogeneous CZTSSe alloys were obtained. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2013.10.001

Web of Science

Scopus

Epitaxial growth of metastable multiferroic AlFeO<inf>3</inf> film on SrTiO<inf>3</inf> (111) substrate Reviewed

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

Applied Physics Letters Vol. 104 ( 8 ) 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

GaFeO3-type AlFeO3 is consisted of oxygen octahedra and tetrahedra containing Al and Fe ions and is known to have a non-centrosymmetric polar structure with space group Pna21. We tried to grow epitaxial GaFeO3-type AlFeO3 films on SrTiO 3 (111) substrates by pulsed laser deposition technique. Both the atomic arrangement of close-packed and the atomic distance of the substrate surface played important roles in stabilizing GaFeO3-type AlFeO 3 on the substrate. Piezoresponse force microscopy measurements clearly showed that GaFeO3-type AlFeO3 films have ferroelectricity at room temperature. In addition, AlFeO3 film also showed pinched-like hysteresis loop with TN ∼ 317 K. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4866798

Web of Science

Scopus

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Papers - TANIGUCHI Hiroki