Faculty Profiles - TANIGUCHI Hiroki

Papers - TANIGUCHI Hiroki

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Thermal Diffusivity of the Mott Insulator Ca2RuO4 in a Non-equilibrium Steady State Reviewed Open Access

Shuji Kawasaki, Akitoshi Nakano, Hiroki Taniguchi, Hai Jun Cho, Hiromichi Ohta, Fumihiko Nakamura, Ichiro Terasaki

Journal of the Physical Society of Japan Vol. 90 ( 6 ) page： 063601 - 063601 2021.6

Thermal Diffusivity of the Mott Insulator Ca₂RuO₄ in a Non-equilibrium Steady State Reviewed

K. Shuji, N. Akitoshi, T. Hiroki, C. H. Jun, O. Hiromichi, N. Fumihiko, I. Terasaki

Journal of the Physical Society of Japan Vol. 90 ( 6 ) page： 63601 - 1-5 2021.6

Unconventional high-temperature ferromagnetic semiconductor PbPd1-x-yFeyLix O2 Reviewed International coauthorship Open Access

Y. He, D. Sato, K. Misawa, D. Nishihara, A. Kimura, A. Nakano, H. Taniguchi, I. Terasaki

Journal of Applied Physics Vol. 129 ( 20 ) page： 203903 2021.5

Fabrication of bismuth silicate Bi2SiO5 ceramics as a potential high-temperature dielectric material Reviewed

K. Sakamoto, M. Hagiwara, H. Taniguchi, S. Fujihara

Journal of Materials Science Vol. 56 ( 14 ) page： 8415 - 8426 2021.5

Size effect of the guest cation on the AlO4 framework in aluminate sodalite-type oxides M8[Al12O24](SO4)2 (M = Sr2+ and Ca2+) in the I43m phase Reviewed

Y. Nakahira, G. Kawamura, T. Wakamatsu, I. Terasaki, H. Taniguchi, Y. Kuroiwa, C. Moriyoshi

Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials Vol. 77 page： 186 - 192 2021.4

Room Temperature Thermoelectric Properties of Isostructural Selenides Ta2PdS6 and Ta2PdSe6 Reviewed Open Access

A. Nakano, U. Maruoka, F. Kato, H. Taniguchi, I. Terasaki

Journal of the Physical Society of Japan Vol. 90 ( 3 ) page： 33702 - 33702 2021.3

Ga-substitution effects on the improper ferroelectric phase transition of Ca8[AlO2]12(MoO4)2 Reviewed Open Access

K. Maruyama, A. Nakano, I. Terasaki, H. Taniguchi

Open Ceramics Vol. 5 2021.3

Coexisting Mechanisms for the Ferroelectric Phase Transition in Li2SrNb2O7 Reviewed

Y. Mochizuki, T. Nagai, H. Shirakuni, A. Nakano, F. Oba, I. Terasaki, H. Taniguchi

Chemistry of Materials Vol. 33 ( 4 ) page： 1257 - 1264 2021.2

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Pseudo-Ruddlesden-Popper-type Li2SrNb2O7 (LSNO), which belongs to a layered perovskite-type family, exhibits a first-order ferroelectric phase transition at 217 K. Our first-principles calculations and dielectric measurements show that Ca-substitution for Sr in LSNO enhances the rotation of NbO6 octahedra and Nb5+ displacements to induce a robustly stabilized ferroelectric P2(1)cn phase. The present study has demonstrated the two coexisting mechanisms in the ferroelectric phase transition of LSNO: the second-order Jahn-Teller effect and the rotational-distortion driven hybrid-improper ferroelectricity. The origin of unique ferroelectric phase transition of LSNO has been clarified to be softening of the zone-boundary Y-2(-) mode. The present study provides a new insight into designing ferroelectricity in layered perovskite-type oxides with the second-order Jahn-Teller effect and the rotations of octahedra.

DOI： 10.1021/acs.chemmater.0c04032

Web of Science

Scopus

Nanoscale structural analysis of Pb(Mg1/3Nb2/3)O3 Reviewed

Y. Yoneda, H. Taniguchi, Y. Noguchi

Journal of Physics: Condensed Matter Vol. 33 ( 3 ) page： 035401 - 035401 2021.1

Lamellar-like nanostructure in a relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3 Reviewed

Y. Sato, S. Fujinaka, S. Yamaguchi, R. Teranishi, K. Kaneko, T. Shimizu, H. Taniguchi, H. Moriwake

Journal of Materials Science Vol. 56 ( 2 ) page： 1231 - 1241 2021.1

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

The nanostructure of relaxor ferroelectric materials has been a central focus for investigating the microscopic origin of their intriguing physical properties. While it is believed that relaxor ferroelectricity is governed by polar nanostructures, such as polar nanoregions or nanodomains, recent studies have indicated the importance of additional mechanisms, such as the competition of ferroelectric/anti-ferroelectric order and the formation of hierarchical nanodomains. This calls for further investigation on the nanostructure. Here, we used conventional, in situ, and atomic-scale electron microscopy to study prototypic relaxor ferroelectrics, Pb(Mg Nb )O (PMN) and Pb(Mg Nb )O –PbTiO (PMN-PT). We found that a lamellar-like nanostructure was present in pure PMN, which had been overlooked in past studies and did not have a strong correlation with the polar nanostructure and the chemically ordered region. Unlike the lamellar-like nanodomains in PMN-PT, the lamellar-like nanostructure in PMN was not coupled with Pb-ion displacement and was not reoriented by the presence of an electric field. The results suggested that the formation of a lamellar-like structure occurs prior to the formation of larger-scale polar order in relaxor ferroelectrics. 1/3 2/3 3 1/3 2/3 3 3

DOI： 10.1007/s10853-020-05417-5

Web of Science

Scopus

Firing Temperature of Ancient Ceramic Shards Estimated by Terahertz Spectroscopy

Niijima S., Taniguchi H., Kawase K.

International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz Vol. 2020-November page： 341 - 342 2020.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz

We propose a novel and accurate method of estimating the firing temperature of ancient ceramics using terahertz (THz) wave technology. The method is based on the firing temperature dependence of the THz-wave characteristics of ceramics. Using this method, the firing temperature of an ancient Arita porcelain shard was estimated at 1240 °C, which is within the firing temperature range estimated from other methods but is more precise.

DOI： 10.1109/IRMMW-THz46771.2020.9370497

Scopus

Improper relaxor state in (Ca1-xSrx)8[Al O2]12(Mo O4)2

Nakamori H., Terasaki I., Taniguchi H.

Physical Review Materials Vol. 4 ( 10 ) 2020.10

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Physical Review Materials

Dielectric and elastic properties of aluminate-sodalite-type oxides, (Ca1-xSrx)8[AlO2]12(MoO4)2 with x=1/16 and 1/4, are investigated in the present study. A well-defined improper ferroelectric phase transition is demonstrated in the composition of x=1/16 by the onset of spontaneous strain and sharp anomalies in the dielectric and elastic responses around 600 K. As the Sr concentration increases to x=1/4, strong frequency dispersion appears in the dielectric and elastic responses, indicating that the system changes into a short-range ordered state. The dielectric and elastic anomalies are found to follow a single Vogel-Fulcher equation over a wide frequency range from 10-1 to 106Hz. The present results suggest an improper relaxor state at the composition of x=1/4, in which polar nanoregions form under spatially heterogeneous strain due to differences in the local coordination environments around Ca and Sr.

DOI： 10.1103/PhysRevMaterials.4.104413

Web of Science

Scopus

Permittivity boosting in "yellow" (Nb plus In) co-doped TiO2

Hiroki Taniguchi, Daiki Sato, Akitoshi Nakano, Ichiro Terasaki

JOURNAL OF MATERIALS CHEMISTRY C Vol. 8 ( 39 ) page： 13627 - 13631 2020.10

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

Unusual effects of post annealing on optical and dielectric properties of (Nb0.5In0.5)(0.01)Ti0.99O2(NITO-1.0%) are reported in the present study. The post-annealing performed under embedding in Al(2)O(3)powder changes the color of a NITO-1.0% single crystal from black to yellow. Furthermore, the apparent increase in the relative permittivity due to the Maxwell-Wagner-Sillars effect, on the order of 10(4), observed in the as-synthesized NITO-1.0% completely disappears after the post-annealing to reveal an intrinsic enhancement of dielectric response due to the co-doping of Nb and In. The relative permittivity of the post-annealed NITO-1.0% uniformly increases by approximately 120 from the original value of pure-TiO(2)over a wide temperature range from 4.2 K to room temperature. A temperature dependence of permittivity in the post-annealed NITO-1.0% shows behavior that is qualitatively identical to that of pure TiO2, indicating that the co-doping gives rise to an additional dielectric response in TiO2, probably through creation of defect complexes with large polarizability. The polarizability of the defect complex is estimated to be two hundred times greater than that of Ti4+, giving a new insight for the design of novel dielectric materials with large permittivity by means of complex defect engineering.

DOI： 10.1039/d0tc03539d

Web of Science

Scopus

Ferroelectric and dielectric properties of improper ferroelectric Ca<inf>8-x</inf>Sr<inf>x</inf>[Al<inf>12</inf>O<inf>24</inf>] (MoO<inf>4</inf>)<inf>2</inf>multilayer capacitors

Hirose S., Usui T., Tanaka M., Katsuya Y., Taniguchi H.

Journal of Applied Physics Vol. 128 ( 9 ) 2020.9

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Physics

Improper ferroelectric Ca8-xSrx[Al12O24](MoO4)2 (x = 0-2) multilayer capacitors (MLCs) were fabricated to study their dielectric and ferroelectric properties for their potential practical applications and reversible switching of electric polarization by an electric field. The substitution of Sr for Ca caused a structural change from polar orthorhombic to non-polar cubic phases at 297 K and decreased the ferroelectric phase transition temperature (Tc). Spontaneous polarization up to ∼0.6 μC/cm2 was performed at 297 K in Ca7.5Sr0.5[Al12O24](MoO4)2 and Ca7Sr[Al12O24](MoO4)2 MLCs by poling with an electric field of 10 MV/m. Furthermore, ferroelectric hysteresis loops from the electric polarization switching were successfully demonstrated in Ca8[Al12O24](MoO4)2 MLCs above 469 K by the application of a high electric field over 50 MV/m, and remnant electric polarization of ∼0.59 μC/cm2 was obtained at 573 K. The results introduce a new avenue for possible applications and new functionalities of improper ferroelectrics with an MLC structure.

DOI： 10.1063/5.0016533

Web of Science

Scopus

Non-equilibrium Steady State in the Mott Insulator Ca2RuO4 Open Access

Ichiro Terasaki, Isuzu Sano, Kosuke Toda, Shuji Kawasaki, Akitoshi Nakano, Hiroki Taniguchi, Hai Jun Cho, Hiromichi Ohta, Fumihiko Nakamura

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 89 ( 9 ) 2020.9

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

We have measured and analyzed the nonlinear conduction of the Mott insulator Ca2RuO4 with square wave and square-pulse currents around room temperature with an infrared camera as a contactless thermometer. By combining the thermal diffusivity measurements, we have found that the temperature increase due to self heating is explained by the conduction of the Joule heat through the sample to the heat bath. We further find a time scale of the nonlinear conduction to be 20 ms, which is consistent with thermal relaxation time of the sample. We propose that a steady dissipation of external energy flow characterizes the non-equilibrium steady state of Ca2RuO4, rather than a steady current flow.

DOI： 10.7566/JPSJ.89.093707

Open Access

Web of Science

Scopus

Non-equilibrium Steady State in the Mott Insulator Ca₂RuO₄

Terasaki Ichiro, Sano Isuzu, Toda Kosuke, Kawasaki Shuji, Nakano Akitoshi, Taniguchi Hiroki, Cho Hai Jun, Ohta Hiromichi, Nakamura Fumihiko

Journal of the Physical Society of Japan Vol. 89 ( 9 ) page： 93707 - 1-5 2020.9

Optical enhancement of dielectric permittivity in reduced lanthanum aluminate Reviewed

Takayuki Nagai, Akihide Kuwabara, Yu Kumagai, Ichiro Terasaki, Hiroki Taniguchi

Physical Review B Vol. 101 ( 18 ) 2020.5

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

© 2020 American Physical Society. When light is absorbed in solids, electrical conductivity is usually enhanced through generation of photodoped conductive carriers, known as photoconduction. Here we show UV-light absorption restrains photoconduction, but markedly enhances dielectric permittivity in a ceramic sample of LaAlO3 with defects introduced deliberately by reduction synthesis. Using systematic dielectric measurements under photoirradiation combined with computational studies for defect formation energies, we explain this unconventional photoinduced phenomenon in terms of photoexcited dipoles: The photoexcited electrons are trapped in in-gap states introduced by oxygen vacancies whereas photoexcited holes are localized in a valence-band maximum. Thus the created electron-hole pair acts as an electric dipole to enhance the dielectric permittivity. This unprecedented photoelectric effect does not only provide an alternative functionality for dielectric materials, but also paves the way for next-generation photoelectronic devices.

DOI： 10.1103/PhysRevB.101.184114

Web of Science

Scopus

Current-induced Giant Lattice Deformation in the Mott Insulator Ca2RuO4 Reviewed

Ryuji Okazaki, Kensuke Kobayashi, Reiji Kumai, Hironori Nakao, Youichi Murakami, Fumihiko Nakamura, Hiroki Taniguchi, Ichiro Terasaki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 89 ( 4 ) 2020.4

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

We report that the volume of an orbital-ordered Mott insulator Ca2RuO4 is purely changed by an electrical current at constant temperature and pressure. The observed giant electromechanical response is an intrinsic non-equilibrium property in currents, not from an extrinsic self-heating effect, as is clearly demonstrated by combined transport and synchrotron radiation X-ray diffraction experiments. The underlying mechanism is ascribed to a suppression of orbital order by currents, significantly differing from conventional piezoelectric or electrostrictive effect in dielectric materials. Our results imply a novel non-equilibrium equation of state, in which an equilibrium quantity is described by a non-equilibrium variable, and thus provide fundamental data for investigating the evolving field of non-equilibrium thermodynamics.

DOI： 10.7566/JPSJ.89.044710

Web of Science

Current-induced Giant Lattice Deformation in the Mott Insulator Ca2RuO4

Okazaki Ryuji, Kobayashi Kensuke, Kumai Reiji, Nakao Hironori, Murakami Youichi, Nakamura Fumihiko, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan Vol. 89 ( 4 ) page： 44710 - 44710 2020.4

Examination of Nonlinear Conductivity on the Excitonic Insulator Candidate Ta2NiSe5

Nakano Akitoshi, Maruoka Urara, Taniguchi Hiroki, Terasaki Ichiro

Journal of the Physical Society of Japan Vol. 89 ( 4 ) page： 45001 - 45001 2020.4

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Papers - TANIGUCHI Hiroki