Faculty Profiles - TANIGUCHI Hiroki

Papers - TANIGUCHI Hiroki

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27pPSB-14 Phonon dynamics in Ba_<0.767>Ca_<0.233>TiO_3

SHIMIZU Takao, FU Desheng, TANIGUCHI Hiroki, TANIYAMA Tomoyasu, ITOH Mitsuru

Meeting Abstracts of the Physical Society of Japan Vol. 64.2.4 ( 0 ) page： 886 2009

Ferroelectricity Triggered in the Quantum Paraelectric AgTaO_3 by Li-substitution Reviewed

谷口博基

Applied Physics Letters vol.95 2009

Tuning the Orthorhombic-Rhombohedral Phase Transition Temperature in Sodium Potassium Niobate by Barium Zirconate Reviewed

谷口博基

Physica Status Solidi-Rapid Research Letters 3(5) page： 142 - 144 2009

Soft-mode Dynamics in the Ferroelectric Phase Transition of Quantum Paraelectric SrTiO_3 Reviewed

谷口博基

Ferroelectrics 379 page： 168 - 176 2009

Ferroelectricity Triggered in the Quantum Paraelectric AgTaO_3 by Li-substitution Reviewed

谷口博基

Applied Physics Letters 95(24) page： 2429041 - 3 2009

Direct observation of the soft mode in the paraelectric phase of PbTiO <inf>3</inf> by confocal micro-Raman scattering Reviewed

Hwee Ping Soon, Hiroki Taniguchi, Yasuhiro Fujii, Mitsuru Itoh, Makoto Tachibana

Physical Review B - Condensed Matter and Materials Physics Vol. 78 ( 17 ) 2008.11

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

The soft mode behavior in PbTiO3 (PT) single crystal has been revisited by our confocal micro-Raman measurements. Contrary to the common understandings, the temperature dependence of soft mode in the cubic PT paraelectric phase was precisely resolved for the first time, owing to the existence of macroscopic size Raman active regions (≥780 nm). By evidently ruling out the possibility of defect-induced Raman scattering, the elasto-optical coupling serves as the most likely mechanism for the occurrence of these Raman active regions. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.78.172103

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Reply to comment on "origin of giant dielectric response in nonferroelectric CaCu<inf>3</inf>Ti<inf>4</inf>O<inf>12</inf>: Inhomogeneous conduction nature probed by atomic force microscopy"

Desheng Fu, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Shin Ya Koshihara

Chemistry of Materials Vol. 20 ( 19 ) page： 6286 - 6287 2008.10

Ferroelectric phase transition of Cd2 Nb2 O7 studied by Raman scattering Reviewed

Hiroki Taniguchi, Takao Shimizu, Hitoshi Kawaji, Tooru Atake, Mitsuru Itoh, Makoto Tachibana

Physical Review B - Condensed Matter and Materials Physics Vol. 77 ( 22 ) 2008.6

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

Cadmium pyroniobate (Cd2 Nb2 O7: CNO) is a recent focus in the ferroelectric materials due to its unusual diffuse-phase transition without any compositional fluctuation, unlike conventional relaxors. In the present study, the critical dynamics of CNO was studied by the confocal micro-Raman scattering. The heavily overdamped soft-mode spectra have been resolved in the ferroelectric phase. The coupled-mode analysis successfully extracted the contribution of the relaxational mode from the overdamped soft mode. The decomposed soft mode clearly shows the Landau-type critical behavior with γ=1. The relaxation was reasonably assigned to the hopping motion of Cd ions from its activation energy of ∼21 meV. The phase transition of CNO, in spite of diffusive characteristics in the dielectric peak, is concluded to be purely driven by the conventional softening of the soft mode, which is heavily overdamped due to the coupling with Cd-hoping mode. © 2008 The American Physical Society.

DOI： 10.1103/PhysRevB.77.224104

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Origin of giant dielectric response in nonferroelectric CaCu <inf>3</inf>Ti<inf>4</inf>O<inf>12</inf>: Inhomogeneous conduction nature probed by atomic force microscopy Reviewed

Desheng Fu, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Shin Ya Koshihara

Chemistry of Materials Vol. 20 ( 5 ) page： 1694 - 1698 2008.3

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

Local probing of conduction behaviors using atomic force microscopy clearly shows that the grain boundary of polycrystalline CaCu3Ti 4O12 is semiconducting. In contrast, the grain is a mixture of semiconducting and insulating regions. This inhomogeneous conductive feature leads to giant dielectric response in CaCu3Ti 4O12. Theoretical analysis demonstrates that the dielectric response follows a typical Debye-type relaxation, and its unusual temperature dependence originates from the thermal activation behavior of free carries within the semiconducting regions in the grain. An effective way to control the electrical properties of CCTO is to control the defect density within a grain rather than the grain boundary. © 2008 American Chemical Society.

DOI： 10.1021/cm0710507

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Successive crystallization of ferroelectric-based BaTi<inf>2</inf>O<inf>5</inf> bulk glass studied by Raman scattering Reviewed

Hiroki Taniguchi, Jianding Yu, Yasutomo Arai, Desheng Fu, Toshirou Yagi, Mitsuru Itoh

Materials Science and Engineering B: Solid-State Materials for Advanced Technology Vol. 148 ( 1-3 ) page： 48 - 52 2008.2

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

Non-isothermal crystallization process of ferroelectric-based BaTi2O5 glass (BTO-glass) is investigated by in situ Raman scattering. The gradual change of Raman spectra clearly shows the successive crystallization of BTO-glass through metastable α and β phases. The increase of volume fractions obtained from the development of spectral intensities is analyzed by the Johnson-Mehl-Avrami formula. The results indicate homogeneous crystallization of α phase and subsequent inhomogeneous crystallization of β phase. Finally specially resolved observation reveals the phase separation of β phase on the surface and BaTi2O5 crystal phase in the inside. © 2007.

DOI： 10.1016/j.mseb.2007.09.030

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Dynamics of the ferroelectric phase transition in 18O-exchanged SrTiO<inf>3</inf> studied by Raman scattering Reviewed

Hiroki Taniguchi, Toshirou Yagi, Mitsuru Itoh

Ferroelectrics Vol. 369 ( 1 PART 3 ) page： 3 - 9 2008

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TAYLOR & FRANCIS LTD

Ferroelectric phase transition of 18O-exchanged SrTiO 3 (STO18) was investigated by Raman scattering as a function of the isotope exchange rate x. The result reasonably indicates the existence of the ideal soft mode-type quantum ferroelectric phase transition in STO18. In the vicinity of the critical concentration (xc = 33%), the coexistence of the paraelectric and ferroelectric regions was newly found, in drastic contrast to the homogeneous ferroelectric phase transition in the strongly exchanged STO18, whose x is sufficiently larger than xc. Near xc, the softening of the soft mode shows unusual rounding as a result of the coexistence. The present result indicates novel phase transition nature in the quantum ferroelectric phase transition of STO18, where dynamic heterogeneity plays an essential role.

DOI： 10.1080/00150190802371242

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25pYE-1 Soft Mode and Phase Transition in Pyrochlore-type Ferroelectric Cd_2Nb_2O_7

Taniguchi H., Shimizu T., Tachibana M., Kawaji H., Atake T., Itoh M.

Meeting Abstracts of the Physical Society of Japan Vol. 63.1.4 ( 0 ) page： 944 2008

First-principles calculations of Soft-mode of CaTiO3

Moriwake Hiroki, Hirayama Tsukasa, Tanaka Isao, Taniguchi Hiroki, Ito Mitsuru, Yue Jin Shan

Preprints of Annual Meeting of The Ceramic Society of Japan Preprints of Fall Meeting of The Ceramic Society of Japan Vol. 2008 ( 0 ) page： 184 - 184 2008

Ferroelectric phase transition of <math display="inline"> <mrow> <msub> <mrow> <mtext>Cd</mtext> </mrow> <mn>2</mn> </msub> <msub> <mrow> <mtext>Nb</mtext> </ Reviewed

Taniguchi Hiroki, Shimizu Takao, Kawaji Hitoshi, Atake Tooru, Itoh Mitsuru, Tachibana Makoto

Physical Review B Vol. 77 ( 22 ) page： 224104 2008

Temperature evolution of the optical phonons in Pb(Ni<inf>1/3</inf>Nb <inf>2/3</inf>)O<inf>3</inf> single crystals studied by Raman scattering Reviewed

Jun Kano, Hiroki Taniguchi, Desheng Fu, Mitsuru Itoh, Seiji Kojima

Ferroelectrics Vol. 367 ( 1 PART 1 ) page： 67 - 72 2008

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TAYLOR & FRANCIS LTD

Raman scattering of lead nickel niobate Pb(Ni1/3Nb 2/3)O3 (PNN) single crystals grown by the flux method has been performed to investigate the temperature dependence of the optical phonons of relaxors. Anomaly of the temperature dependence of the Raman intensity at 780 cm-1 was observed. Polar microregions promote the growth of volume gradually above the Curie temperature (∼170 K), and then freeze around 200 K. From the extrapolation of the temperature dependence of the depolarization ratio, we tried to estimate Burns temperature.

DOI： 10.1080/00150190802365962

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Piezoelectric properties of lithium modified silver niobate perovskite single crystals Reviewed

Desheng Fu, Makoto Endo, Hiroki Taniguchi, Tomoyasu Taniyama, Shin Ya Koshihara, Mitsuru Itoh

Applied Physics Letters Vol. 92 ( 17 ) 2008

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

We report the growth and the piezoelectric properties of lead-free perovskite single crystals of Ag1-x Lix Nb O3. It possesses a rhombohedral structure with high ferroelectric phase transition (Tc =548 K for x=0.086) and large spontaneous polarization (Ps ∼40 μC cm2 for x=0.062) along the 〈111〉c direction of pseudocubic perovskite structure for x>0.05-0.06. High quasistatic d33 ∼210 pCN and low dielectric constant have lead to a very large value of piezoelectric voltage constant g33 ∼53.9× 10-3 VmN for the 〈001〉c -cut crystal of this simple perovskite. It has been shown that Li substitution might enhance the piezoelectric coefficient of the crystal. The excellent piezo-/ferroelectricity of this system are considered to be facilitated by the strong polarization nature of both Ag and Li in the perovskite structure. Our findings may stimulate further interests in the development of lead-free piezoelectrics. © 2008 American Institute of Physics.

DOI： 10.1063/1.2918837

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Ferroelectricity in perovskite-type oxides Reviewed

Mitsuru Itoh, Hiroki Taniguchi

Ferroelectrics Vol. 369 ( 1 PART 3 ) page： 127 - 132 2008

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TAYLOR & FRANCIS LTD

Ferroelectricity in perovskite-related oxides was briefly reviewed mainly from the view point of crystal chemistry. Tolerance factor, t, for perovsikte oxides clearly discriminates the dielectric properties of them, except for KTaO. B-site off-center and BO6 tilting become dominant for t > 1 and t < 1, respectively. Only BaZrO3 and SrTiO3 sit on t = 1.00. A-O covalent bonding seems essential for the evolution of ferroelectricity in ABO3 perovskites, especially for the compounds with t < 1.

DOI： 10.1080/00150190802377918

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21aVE-9 First-Principles Study on the Ferroelectric Phase Transition of CdTiO_3

Moriwake Hiroki, Hirayama Tsukasa, Tanaka Isao, Taniguchi Hiroki, Ito Mitsuru, Shan Yue Jin

Meeting Abstracts of the Physical Society of Japan Vol. 63.2.4 ( 0 ) page： 870 2008

22aVE-7 A Novel Low-Energy Excitation in PbTiO_3 as an Origin of Central Peak

Taniguchi Hiroki, Tachibana Makoto, Itoh Mitsuru

Meeting Abstracts of the Physical Society of Japan Vol. 63.2.4 ( 0 ) page： 884 2008

Comprehensive Structural Study of Glassy and Metastable Crystalline BaTiO Reviewed

谷口博基

Chemistry of Materials 21 page： 259 - 263 2008

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Papers - TANIGUCHI Hiroki