Faculty Profiles - TANIGUCHI Hiroki

Papers - TANIGUCHI Hiroki

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High temperature stability of the dielectric and insulating properties of Ca(Ti, Zr)SiO<inf>5</inf> ceramics Reviewed

Junichi Kimura, Hiroki Taniguchi, Takashi Iijima, Takao Shimizu, Shintaro Yasui, Mitsuru Itoh, Hiroshi Funakubo

Applied Physics Letters Vol. 108 ( 6 ) 2016.2

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

© 2016 AIP Publishing LLC. Useful dielectric properties for high-temperature ceramic capacitors are demonstrated in a non-perovskite oxide, Ca(Ti0.85 Zr0.15)SiO5, which is mainly composed of one-dimensional chains of oxygen octahedra that are mutually linked by SiO4 tetrahedra. Its dielectric constant and low temperature coefficient of capacitance were found to be 43 and -102 ppm/K, respectively, over the wide temperature range of 300-780 K. The high insulating performance was also indicated by the high resistivity, exceeding 1011 Ω cm up to 523 K. The systematic dielectric measurements for Ca(Ti1-x Zrx)SiO5 as functions of the composition and temperature indicate that the suppression of the anti-ferroelectric phase transition of CaTiSiO5 by Zr4+-substitution is a key to improve the temperature-stability and the high-resistivity in Ca(Ti1-x Zrx)SiO5. The present results shed light on the development of a designing principle for ceramic capacitors for the high-temperature use.

DOI： 10.1063/1.4941803

Web of Science

Scopus

Optical conductivity of layered calcium cobaltate Ca<inf>3</inf>Co<inf>4</inf>O<inf>9</inf> Reviewed

Kenji Tanabe, Ryuji Okazaki, Hiroki Taniguchi, Ichiro Terasaki

Journal of Physics Condensed Matter Vol. 28 ( 8 ) page： 085601 2016.1

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

© 2016 IOP Publishing Ltd. We report the optical properties of layered calcium cobaltate, Ca3Co4O9, which is regarded as a promising candidate for use as a thermoelectric material. The optical conductivity shows three broad peaks related to the inter-band transition below 4 eV, which are quite similar to those in the spectra of NaxCoO2. This similarity implies that the CoO2 layer, which is an essential unit for both Ca3Co4O9 and NaxCoO2, is dominant in the energy band structure below 4 eV. In addition, we estimate the effective carrier number per Co site and find similarity between the CoO2 layers of Ca3Co4O9 and Na0.75CoO2, which is consistent with the similarity in their Seebeck coefficients. To discuss the contribution of the rocksalt-type Ca2CoO3 layer in Ca3Co4O9, we propose the concept of optical sheet conductivity in the layered materials and estimate its value in the Ca2CoO3 layer. A comparison with the spin-polarized band calculation of the LDA + Hubbard U formalism with U = 5 eV suggests that the Ca2CoO3 layer has the inter-band transition of 2.6 eV in the spin-down band structure. Evaluation of the valences of Co 3d orbitals indicates the existence of charge transfer from the Ca2CoO3 layer to the CoO2 layer and mixing of Co3+ and Co4+ in the CoO2 layer, which may be the origin of the large thermoelectric effect.

DOI： 10.1088/0953-8984/28/8/085601

Web of Science

Scopus

PubMed

Ferromagnetic cluster glass phase embedded in a paramagnetic and metallic host in non-uniform magnetic system CaRu<inf>1-x</inf>Sc<inf>x</inf>O<inf>3</inf> Reviewed

Takafumi D. Yamamoto, Atsuhiro Kotani, Hiroshi Nakajima, Ryuji Okazaki, Hiroki Taniguchi, Shigeo Mori, Ichiro Terasaki

Journal of the Physical Society of Japan Vol. 85 ( 3 ) page： 034711 2016

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

© 2016 The Physical Society of Japan. We have investigated both static and dynamic magnetic properties of polycrystalline CaRu1-xScxO3 system in order to clarify the role of Sc ions as a disorder for magnetic ordering. We have observed typical features of a ferromagnetic cluster glass state below around 40 K: (i) a broad, frequency-dependent peak in the ac magnetic susceptibility, (ii) a slow relaxation of the magnetization, and (iii) a continuous increase in the dc magnetic susceptibility in field cooling process. The composition dependence of characteristic parameters for the cluster glass state suggests that chemical segregation can hardly explain the clustering mechanism. We propose a possible picture that the ferromagnetic clusters are distributed uniformly and form the glassy state embedded in the paramagnetic and metallic host of CaRuO3.

DOI： 10.7566/JPSJ.85.034711

Web of Science

Scopus

CiNii Research

Heterovalent Pb-substitution in ferroelectric bismuth silicate Bi<inf>2</inf>SiO<inf>5</inf> Reviewed

Hiroki Taniguchi, Tomohiro Nakane, Takayuki Nagai, Chikako Moriyoshi, Yoshihiro Kuroiwa, Akihide Kuwabara, Masaichiro Mizumaki, Kiyofumi Nitta, Ryuji Okazaki, Ichiro Terasaki

Journal of Materials Chemistry C Vol. 4 ( 15 ) page： 3168 - 3174 2016

Publishing type：Research paper (scientific journal)

© The Royal Society of Chemistry 2016. Systematic tuning of the ferroelectric phase transition in Bi2SiO5 was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi2O2 layers, resulting in the nominal composition (Bi1-x3+Pbx2+)2SiO5-x. The oxygen vacancies were found to induce local disordering of SiO4 tetrahedral chains, sandwiched between the Bi2O2 layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi2SiO5.

DOI： 10.1039/c6tc00584e

Scopus

Heterovalent Pb-substitution in ferroelectric bismuth silicate Bi2SiO5 Reviewed

Hiroki Taniguchi, Tomohiro Nakane, Takayuki Nagai, Chikako Moriyoshi, Yoshihiro Kuroiwa, Akihide Kuwabara, Masaichiro Mizumaki, Kiyofumi Nitta, Ryuji Okazaki, Ichiro Terasaki

JOURNAL OF MATERIALS CHEMISTRY C Vol. 4 ( 15 ) page： 3168 - 3174 2016

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

Systematic tuning of the ferroelectric phase transition in Bi2SiO5 was demonstrated using element substitution, where nominally heterovalent Pb was successfully substituted for Bi up to 20%. Comprehensive studies using powder X-ray diffraction analysis, dielectric measurements, X-ray absorption spectroscopy, and first-principles calculations revealed that charge compensation for heterovalent substitution was achieved via introduction of a considerable number of oxygen vacancies in Bi2O2 layers, resulting in the nominal composition (Bi1-x Pb-3+(x)2+)(2)SiO5-x. The oxygen vacancies were found to induce local disordering of SiO4 tetrahedral chains, sandwiched between the Bi2O2 layers, leading to a decrease in the ferroelectric phase transition temperature and broadening of the phase transition in Bi2SiO5.

DOI： 10.1039/c6tc00584e

Web of Science

Broad-band Micro-light-scattering Study on Stuffed-sodalite (CaxSr1-x )8 (Al O2)12 (WO4 )2

Katayama D., Fujii Y., Koreeda A., Taniguchi H., Terasaki I.

Meeting Abstracts of the Physical Society of Japan Vol. 71 ( 0 ) page： 2553 - 2553 2016

Nonlinear Seebeck Effect in Ca2RuO4

Toda K., Tanabe K., Taniguchi H., Okazaki R., Nakamura F., Terasaki I.

Meeting Abstracts of the Physical Society of Japan Vol. 71 page： 1859 - 1859 2016

Photo-dielectric effects in reduced LaAlO3

Nagai T., Tanabe K., Terasaki I., Kuwabara A., Taniguchi H.

Meeting Abstracts of the Physical Society of Japan Vol. 71 page： 2514 - 2514 2016

Susceptibility of Co ions doped in Ba3Zn1Ru2O9

Hara Y., Matsushita T., Wada N., Igarashi T., Yatagai R., Tanabe K., Taniguchi H., Terasaki I.

Meeting Abstracts of the Physical Society of Japan Vol. 71 page： 1494 - 1494 2016

Co-responsive dielectric materials: toward novel functionalities over optical, mechanical, and dielectric properties

Taniguchi Hiroki

Meeting Abstracts of the Physical Society of Japan Vol. 71 page： 2587 - 2588 2016

Effects of Magnetic Fluctuation on Transport Properties in CaRu1-xScxO3

Yamamoto T. D., Yatagai R., Tanabe K., Okazaki R., Taniguchi H., Yasui Y., Iguchi S., Sasaki T., Terasaki I.

Meeting Abstracts of the Physical Society of Japan Vol. 71 page： 1002 - 1002 2016

Transport and Magnetic Properties in CaPd3-xCuxO4(0≦x≦2.4)

Misawa K., Tanabe K., Taniguchi H., Terasaki I.

Meeting Abstracts of the Physical Society of Japan Vol. 71 page： 1000 - 1000 2016

Effects of the Ir impurity on the thermodynamic and transport properties of Ba<inf>4</inf>Ru<inf>3</inf>O<inf>10</inf> Reviewed

Taichi Igarashi, Ryuji Okazaki, Hiroki Taniguchi, Yukio Yasui, Ichiro Terasaki

Journal of the Physical Society of Japan Vol. 84 ( 9 ) page： 094601 2015.9

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

© 2015 The Physical Society of Japan. We report the effects of Ir impurity on the physical properties of Ba4Ru3-xIrxO10 (0 ≤ x ≤ 0.5) which is composed of three face-shared RuO6 octahedra (Ru trimer). We discuss the origin of the unique electronic phase transition from paramagnetic metal to antiferromagnetic insulator at 105K in terms of hybridized orbitals of Ru 4d in the Ru trimer. From the magnetic susceptibility and the specific heat, the transition temperature is found to decrease more remarkably than is expected in typical diluted magnets and is hardly discernible at around x = 0.5, while the magnetic interaction only decreases slightly with x. This implies that the transition is not driven by magnetic interaction. In contrast, the hump due to the phase transition still remains in the Seebeck coefficient for x = 0.5, which means that the charge gap still remains as a short-range order. Since the charge gap originates from the 4d hybridization in the Ru trimer, intra-trimer charge transfer is likely to dominate the transition.

DOI： 10.7566/JPSJ.84.094601

Web of Science

Scopus

CiNii Research

Effects of the Ir Impurity on the Thermodynamic and Transport Properties of Ba4Ru3O10

Igarashi Taichi, Okazaki Ryuji, Taniguchi Hiroki, Yasui Yukio, Terasaki Ichiro

Journal of the Physical Society of Japan Vol. 84 ( 9 ) page： 94601 - 94601 2015.9

Strong anisotropy of ferroelectricity in lead-free bismuth silicate Reviewed

Daehee Seol, Hiroki Taniguchi, Jae Yeol Hwang, Mitsuru Itoh, Hyunjung Shin, Sung Wng Kim, Yunseok Kim

Nanoscale Vol. 7 ( 27 ) page： 11561 - 11565 2015.7

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

© The Royal Society of Chemistry 2015. Bismuth silicate (Bi2SiO5) was recently suggested as a potential silicate based lead-free ferroelectric material. Here, we show the existence of ferroelectricity and explore the strong anisotropy of local ferroelectricity using piezoresponse force microscopy (PFM). Domain structures are reconstructed using angle-resolved PFM. Furthermore, piezoresponse hysteresis loops and piezoelectric coefficients are spatially investigated at the nanoscale. The obtained results confirm the existence of ferroelectricity with strong c-axis polarization. These results could provide basic information on the anisotropic ferroelectricity in Bi2SiO5 and furthermore suggest its considerable potential for lead-free ferroelectric applications with silicon technologies.

DOI： 10.1039/c5nr03161c

Web of Science

Scopus

PubMed

Effects of element substitution on the pyroelectric phase transition of stuffed-tridymite-type BaZnGeO<inf>4</inf> Reviewed

Takayuki Nagai, Shinichiro Asai, Ryuji Okazaki, Ichiro Terasaki, Hiroki Taniguchi

Solid State Communications Vol. 219 page： 12 - 15 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

© 2015 Elsevier Ltd. Abstract Effects of element substitution on the phase transition between different pyroelectric phases of the stuffed-tridymite-type oxide, BaZnGeO4, are examined by dielectric measurements on BaZn1-xMxGeO4 (M=Ni, Co, and Mn) with x=0.05 and 0.10. The Ni2+-substitution is found to suppress strongly the phase transition, in marked contrast to the cases of Co2+ and Mn2+ that have only subtle influences on the transition temperature. Internal distortions of MO4 tetrahedra due to the Jahn-Teller effect might play a major role in the variation of transition temperature induced by the element substitution.

DOI： 10.1016/j.ssc.2015.06.011

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Scopus

Structural changes and microstructures of Ba<inf>1-x</inf>Sr<inf>x</inf>Al<inf>2</inf>O<inf>4</inf> for 0 < x < 0.4

E. Tanaka, Y. Ishii, H. Tsukasaki, S. Mori, M. Osada, H. Taniguchi, Y. Sato, Y. Kubota

Journal of the Korean Physical Society Vol. 66 ( 9 ) page： 1355 - 1358 2015.5

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

© 2015, The Korean Physical Society. We have investigated the structural changes and the microstructures of Ba1-xSrxAl2O4 for 0 < x < 0.4 by using transmission electron microscope (TEM) and synchrotron radiation powder X-ray diffraction experiments. The TEM experiments revealed the existence of a structural phase boundary at approximately x = 0.1, at which the superlattice reflection spots at the 1/2 0 0 -type positions change into diffuse streaks along three equivalent <110> directions in the hexagonal structure. In addition, real-space images of Ba1-xSrxAl2O4 for 0 < x < 0.4 reveal that BaAl2O4 should be characterized as a modulated structure with triple-q modulation vectors along the <110> directions and on the other hand, Ba1-xSrxAl2O4 for 0.1 < x < 0.4 be characterized as an intermediate (precursor) state with a rigid unit mode due to structural instability. These experimental results implied that the partial substitution of Sr2+ for Ba2+ should suppress a structural instability due to the AlO4 tetrahedral network and decrease the structural phase transition temperature.

DOI： 10.3938/jkps.66.1355

Web of Science

Scopus

Photo-Seebeck effect in ZnS Reviewed

Yuuka Shiraishi, Ryuji Okazaki, Hiroki Taniguchi, Ichiro Terasaki

Japanese Journal of Applied Physics Vol. 54 ( 3 ) 2015.3

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

© 2015 The Japan Society of Applied Physics. To explore the thermoelectric transport nature of photo-excited carriers, the electrical conductivity and the Seebeck coefficient are measured under ultraviolet illumination in the wide-gap semiconductor ZnS near room temperature. The conductivity increases linearly as against the photon flux density with little dependence on temperature, indicating the conduction under illumination is mostly governed by the photo-doped carriers. We have found that, in high contrast to the temperature-insensitive photoconductivity, the temperature dependence of the Seebeck coefficient is dramatically varied by illumination, which is unexplained from a simple photo-doping effect for one majority carrier. Such a distinct difference in the transport quantities is rather understood within a two-carrier model, in which only the Seebeck coefficient is strongly affected by photo-excited minority carriers. The present result is also compared with earlier reports of the photo-Hall experiments to discuss the underlying photo-transport mechanism.

DOI： 10.7567/JJAP.54.031203

Web of Science

Scopus

Non-uniform magnetic system driven by non-magnetic ion substitution in CaRu<inf>1-x</inf>Sc<inf>x</inf>O<inf>3</inf>: Two-component analysis Reviewed

Takafumi D. Yamamoto, Ryuji Okazaki, Hiroki Taniguchi, Ichiro Terasaki

Journal of the Physical Society of Japan Vol. 84 ( 1 ) page： 014708 2015.1

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

© 2015 The Physical Society of Japan. We have studied magnetic and transport properties in polycrystalline CaRu1-xScxO3 for 0 ≤ x ≤ 0.20 in order to clarify the substitution effects of a non-magnetic trivalent ion. We find that a ferromagnetic transition with Tc ~ 30K is observed in Sc-substituted samples. The composition dependence of the Curie-Weiss temperature ΘCW implies that the magnetic susceptibility has a paramagnetic contribution with negative ΘCW and a ferromagnetic contribution with positive ΘCW. The field dependence of magnetization at 2K is also understood as a summation of the ferromagnetic and paramagnetic components. These results suggest that CaRu1-xScxO3 is a non-uniform magnetic system. The relationship between the ferromagnetic ordering and the transport properties is also discussed.

DOI： 10.7566/JPSJ.84.014708

Yamamoto Takafumi D., Okazaki Ryuji, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan Vol. 84 ( 1 ) page： 14708 - 14708 2015.1

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Papers - TANIGUCHI Hiroki