Faculty Profiles - TANIGUCHI Hiroki

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 Vol. 82 ( 10 ) page： 104603 - 104603 2013.10

X-ray crystal structure analysis and Ru valence of Ba<inf>4</inf>Ru <inf>3</inf>O<inf>10</inf> single crystals Reviewed

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

Journal of the Physical Society of Japan Vol. 82 ( 10 ) page： 104603 2013.10

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

We present a single-crystalline x-ray diffraction study on Ba4Ru3O10 consisting of corner-shared Ru3O12 trimers. The crystal structure is redetermined from 78 to 300K across an antiferromagnetic transition at 105 K. The orthorhombic symmetry (Cmca, space group No. 64) is preserved at all temperatures measured. This structure presents exceptionally long Ru-O distances characterized by a significant distribution within the Ru 3O12 trimer. A bond valence sum calculation suggests that the charge disproportionation within the Ru3O12 trimer emerges even at room temperature, which we ascribe to molecular orbital formation in the Ru3O12 trimer, as supported by the results of recent theoretical calculations. On the basis of the analyzed crystal structure, the electronic states and the nature of the phase transition at 105K are discussed. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.104603

Confocal micro-Raman imaging on 180°-domain structure in periodically poled stoichiometric LiNbO<inf>3</inf> Reviewed

Hiroki Taniguchi, Yasuhiro Fujii, Mitsuru Itoh

Journal of the Ceramic Society of Japan Vol. 121 ( 1416 ) page： 579 - 582 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

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 NbO bond, while there was no significant change in Li-ion related modes. NbO 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. © 2013 The Ceramic Society of Japan.

DOI： 10.2109/jcersj2.121.579

Ferroelectricity driven by twisting of silicate tetrahedral chains Reviewed

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

Angewandte Chemie - International Edition Vol. 52 ( 31 ) page： 8088 - 8092 2013.7

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

A lead-free ferroelectric: The occurrence of ferroelectricity is demonstrated in a silicate-based compound (Bi2SiO5, see picture), by direct observation of polarization switching. The mechanism of ferroelectricity in Bi2SiO5 has been studied by Raman scattering, transmission electron microscopy, X-ray powder diffraction, and first-principles calculations. The observed ferroelectricity stems from twisting of the one-dimensional SiO4 tetrahedral chain. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/anie.201302188

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

PubMed

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 Vol. 82 ( 7 ) page： 74721 - 74721 2013.7

Growth and characterization of Cu<inf>2</inf>ZnSnS<inf>4</inf> single crystals Reviewed

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

Physica Status Solidi (A) Applications and Materials Science Vol. 210 ( 7 ) page： 1328 - 1331 2013.7

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-V C H VERLAG GMBH

We investigated the growth condition of high-quality Cu 2ZnSnS4 (CZTS) single crystal by traveling heater method (THM) which is one of the solution-based growth methods. We selected Sn as solvent because it is a constituent element of CZTS with low melting point. The solubility of CZTS in Sn solvent was approximately 0.01 mol% at 600 °C and 0.28 mol% at 1000 °C. It is found that CZTS is soluble in Sn solvent, which is similar to CuGaS2 in In solvent. The Sn solutions saturated with CZTS solutes less than 60 mol% were separated with two phases, less than 30 mol% solutions were CZTS and Sn phases and solutions from 30 to 60 mol% were CZTS and SnSx compound phases. It is impossible to grow CZTS single crystal from less than 60 mol% Sn solutions, because secondary phases located at the bottom of the ampoule and interfered with single crystal growth. Optimum growth condition of CZTS was determined based on CZTS-Sn phase diagram, which was growth temperature 900 °C and X = 70 mol% solution. The electrical properties of CZTS single crystal were observed along the growth direction and it can be clearly seen that the electrical properties are homogeneous along the growth direction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.201200815

Ultrafast real space dynamics of photoexcited state in a layered perovskite-type spin crossover oxide La<inf>1.5</inf>Sr<inf>0.5</inf>CoO <inf>4</inf> Reviewed

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 Vol. 82 ( 7 ) page： 074721 2013.7

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

Ultrafast optical responses were investigated using a fs laser system on a layered perovskite-type cobalt oxide, La1.5Sr0.5CoO 4 with a checkerboard-type charge ordering. To investigate the spatial variation of the photoexcited state, we measured the transient changes of three independent optical quantities, i.e., transmittance, reflectivity, and backside reflectivity, as well as their fluence dependence at 0.25 eV. Using the numerical calculations based on Maxwell's equations, we calculated not only the dielectric constant but also the decay length of the photoexcited region (L) and analyzed the real-space dynamics of the photoexcited area in terms of the fluence and time dependence of L. With the above information on the time dependence of L and Kramers-Kronig analysis, we numerically calculated the transient optical conductivity spectra, which showed instantaneous formation of a polaron-like absorption peak in the midinfrared region. A 10 fs pump-probe reflection measurement revealed that the photoexcited state occurs within the time resolution (≈10 fs). The time profile of the reflectivity is accompanied with an oscillation assigned as a breathing phonon mode in the CoO2 layer observed in Raman spectroscopy. Analyses of the decay time and the frequency revealed that the photoirradiation melted the charge ordering in La1.5Sr0.5CoO4. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.074721

Electric-voltage control of magnetism in Fe/BaTiO<inf>3</inf> heterostructured multiferroics Reviewed

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

Journal of Applied Physics Vol. 113 ( 17 ) page： 17C701/1 - 3 2013.5

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST 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

Other Link： http://orcid.org/0000-0003-3683-5416

Comparative study of phase transitions in BaTiO<inf>3</inf> thin films grown on (001)- and (110)-oriented SrTiO<inf>3</inf> substrate Reviewed

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

Journal of Physics Condensed Matter Vol. 25 ( 13 ) 2013.4

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

An increase of the Curie temperature, TC, was demonstrated for BaTiO3 (BTO) epitaxial thin films grown by a pulsed laser deposition technique on (001) and (110) SrTiO3 (STO) substrates. The T C values for the BTO films on (001) and (110) STO were determined, from the temperature dependence of the lattice constants, to be 720 and 550 K, respectively, both of which are higher than that for bulk BTO. The increase of TC for the film on (001) BTO is suggested to stem from a large tetragonal deformation with a tetragonality of ∼1.02 due to a two-dimensional clamping effect, which persists even in the paraelectric phase. That for the (110) BTO film, on the other hand, could be caused by a one-dimensional clamping effect due to uniaxial strain. © 2013 IOP Publishing Ltd.

DOI： 10.1088/0953-8984/25/13/132001

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

Vol. 6 ( 1 ) page： "015803-1"-"015803-3" 2013.1

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

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

APPLIED PHYSICS EXPRESS Vol. 6 ( 1 ) 2013.1

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

An unconventional pseudo tetragonal crystal structure is demonstrated in a BaTiO3 (BTO) epitaxial thin film grown on a (110) SrTiO3 (STO) substrate by pulsed laser deposition. The crystal structure of the BTO film, one of whose principal axes is shorter than the other, is markedly different from the bulk tetragonal structure. The pseudo tetragonal structure would be caused by the nearly uniaxial strain due to the different strain relaxation along the [001] and [110] axes. An irregular 90 degrees domain structure observed by piezo response force microscopy (PFM) is understood on the basis of a possible small elastic strain at the domain boundary in the pseudo tetragonal crystal structure. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.015803

Unconventional Structure in BaTiO3 Thin Film Grown on （110）SrTiO3 Substrate

SHIMIZU Takao, TANIGUCHI Hiroki, TANIYAMA Tomoyasu, ITOH Mitsuru

Nihon Kessho Gakkaishi Vol. 55 ( 5 ) page： 290 - 295 2013

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Crystallographic Society of Japan

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

High photodegradation efficiency of Rhodamine B catalyzed by bismuth silicate nanoparticles Reviewed

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

Catalysis Communications Vol. 39 page： 65 - 69 2013

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

Bismuth silicate Bi2SiO5 (BSO) nanoparticles were synthesized through a hydrothermal reaction followed by heat treatment. Kinds of characteristic methods were employed to study the phase, morphology and photophysical properties of BSO. The as-prepared BSO exhibited high photocatalytic activity and good photodegradation repeatability in the decomposition of Rhodamine B (RhB) dyes under simulated sunlight irradiation. The experimental results by using different scavengers demonstrate that the photogenerated h+ and e- radicals play an interactional role in the degradation of RhB dyes. BSO nanocrystals could be a promising photocatalysis in water purification industry. © 2013 Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.catcom.2013.04.029