Faculty Profiles - TANIGUCHI Hiroki

Papers - TANIGUCHI Hiroki

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Origin of Giant Dielectric Response in Nonferroelectric CaCu_3Ti_4O_12 : Inhomogeneous Conduction Nature Probed by Atomic Force Microscopy Reviewed

谷口博基, 谷山智康

Chemistry of Materials vol.20 page： 1694 - 1698 2008

Ferroelectricity in Perovskite-Type Oxides Reviewed

谷口博基

Ferroelectrics 369 page： 127 - 132 2008

Ferroelectric Phase Transition of Cd_2Nb_2O_7 Studied by Raman Scattering Reviewed

谷口博基

Physical Review B vol.77 2008

Dynamics of the Ferroelectric Phase Transition in ^<18>O-exchanged SrTiO_3 Studied by Raman Scattering Reviewed

谷口博基

Ferroelectrics 369 page： 3 - 9 2008

Direct Observation of the Soft Mode in the Paraelectric Phase of PbTiO_3 by Confocal Micro-Raman Scattering Reviewed

谷口博基

Physical Review B vol.78 2008

Direct Observation of the Soft Mode in the Paraelectric Phase of PbTiO_3 by Confocal Micro-Raman Scattering Reviewed

谷口博基

Physical Review B 78 2008

Critical soft-mode dynamics and unusual anticrossing in CdTi O3 studied by Raman scattering Reviewed

Hiroki Taniguchi, Yue Jin Shan, Hajime Mori, Mitsuru Itoh

Physical Review B - Condensed Matter and Materials Physics Vol. 76 ( 21 ) 2007.12

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

The ferroelectric phase transition and the critical soft-mode behavior of CdTi O3 were investigated by confocal micro-Raman scattering. The soft mode softens toward zero frequency at Tc with the underdamped vibrational state, indicating ideal displacive-type ferroelectric phase transition. The continuous development of the spectra of ferroelectric modes clarified the second-order phase transition of CdTi O3. The soft mode undergoes an unusual splitting during the softening, which is reasonably explained by anticrossing between the soft mode and the different symmetry mode due to the local symmetry breakdown into the triclinic one. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevB.76.212103

Scopus

Critical soft-mode dynamics and unusual anticrossing in CdTiO3 studied by Raman scattering Reviewed

Hiroki Taniguchi, Yue Jin Shan, Hajime Mori, Mitsuru Itoh

PHYSICAL REVIEW B Vol. 76 ( 21 ) 2007.12

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

The ferroelectric phase transition and the critical soft-mode behavior of CdTiO3 were investigated by confocal micro-Raman scattering. The soft mode softens toward zero frequency at T-c with the underdamped vibrational state, indicating ideal displacive-type ferroelectric phase transition. The continuous development of the spectra of ferroelectric modes clarified the second-order phase transition of CdTiO3. The soft mode undergoes an unusual splitting during the softening, which is reasonably explained by anticrossing between the soft mode and the different symmetry mode due to the local symmetry breakdown into the triclinic one.

DOI： 10.1103/PhysRevB.76.212103

Web of Science

Light scattering study of the phase transition in quantum paraelectric strontium titanate

Yagi T., Takesada M., Taniguchi H., Itoh M.

JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. 51 ( 2 ) page： 798-803 2007.8

Light scattering study of the phase transition in quantum paraelectric strontium titanate Reviewed

T. Yagi, M. Takesada, H. Taniguchi, M. Itoh

Journal of the Korean Physical Society Vol. 51 ( 2 PART I ) page： 798 - 803 2007.8

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

New features of the ferroelectric phase transition are found by using light scattering studies on quantum paraelectric SrTi16O3 (STO16) and its oxygen-isotope exchanged compound SrTi18O3 (STO18). The ferroelectric Eu mode observed by using high-resolution spectroscopy with interferometry shows a perfect softening at the phase transition point of the ferroelectric STO18-95, where 95 % of the oxygen atoms are replaced by the oxygen isotope 18O. The phase transition is concluded to be an ideal displacive-type transition accompanied with the complete freezing of the Slater-type polar mode. The role of the substituted 18O atoms is elucidated in more detail by using low-frequency Raman scattering below 1 K with a triple monochromator. The dynamical inhomogeneity enhanced by the inhomogeneous distribution of 18O atoms plays an essential role in quantum paraelectric STO18 where the concentration of 18O is less than the critical value of 33 %. Both the decrease in the frequency of the polar modes as a mass effect and the enhancement of the dynamical inhomogeneity take place cooperatively in the quantum paraelectric-ferroelectric phase transition in STO18.

DOI： 10.3938/jkps.51.798

Web of Science

Scopus

Ideal soft mode-type quantum phase transition and phase coexistence at quantum critical point in O18-exchanged SrTiO3 Reviewed

Hiroki Taniguchi, Mitsuru Itoh, Toshirou Yagi

Physical Review Letters Vol. 99 ( 1 ) page： 017602 2007.7

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

The quantum ferroelectric phase transition of O18-exchanged SrTiO3 (x% exchanged SrTiO3 is abbreviated as STO18-x) was investigated by Raman scattering as a function of x. The result indicates the ideal soft mode-type quantum ferroelectric phase transition of STO18-x, where the O18 exchange enhances the softening of the soft mode by the suppression of quantum fluctuation. In the vicinity of the quantum critical point (x∼xc=33%), the system results in the ferroelectric-paraelectric phase coexistence state, in clear contrast to the homogeneous ferroelectric phase in STO18-x, whose x is sufficiently larger than xc. Simultaneously, the softening of the soft mode becomes strongly rounded with the underdamped oscillation. The present result indicates that the sensitivity of the soft phonon vibration to the mass disorder is dramatically enhanced in the vicinity of the quantum critical point. © 2007 The American Physical Society.

DOI： 10.1103/PhysRevLett.99.017602

Web of Science

Scopus

PubMed

Recent topics on the light scattering study of ferroelectrics Reviewed

Toshirou Yagi, Masaki Takesada, Hiroki Taniguchi, Mitsuru Itoh

Ferroelectrics Vol. 355 ( 1 PART 1 ) page： 3 - 12 2007

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

Recent light scattering studies on the oxygen-isotope exchanged strontium titanate SrTi18O3 (STO18) have reported a new feature of the ferroelectric phase transition; a perfect softening of the polar E u mode at TC has been found in 95% exchanged STO18 by a high-resolution interferometric spectroscopy. The frequency of the polar E u mode becomes zero at TC without any anomalous increase of the attenuation. The phase transition mechanism is an ideal displacive type induced by the instability of the Slater-type polar mode. The Raman scattering at ultra-low temperature using the 3He cryostat elucidates importance of inhomogeneity enhanced by the distribution of 18O atoms in STO18-x, where x is the concentration of 18O.

DOI： 10.1080/00150190701515790

Web of Science

Scopus

22pTE-3 Displacive-Type Ferroelectric Phase Transition and the Soft Mode in CdTiO_3 Open Access

Taniguchi Hiroki, Shan Yue Jin, Mori Hajime, Itoh Mitsuru

Meeting Abstracts of the Physical Society of Japan Vol. 62.2.4 ( 0 ) page： 996 2007

Conductive boundary layer in CaCu <inf>3</inf>Ti <inf>4</inf>O <inf>12</inf> with giant-dielectric-response Reviewed

Desheng Fu, Yosuke Arima, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Itoh, Jianding Yu, Shin Ya Koshihara

Ferroelectrics Vol. 347 page： 140 - 144 2007

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

Dense polycrystalline samples of CaCu3Ti4O12 (CCTO) were prepared by solid-state reaction method under a high hydraulic pressure of 700 MPa, and characterized by X-ray diffraction, scanning electron microscopy and atomic force microscopy (AFM). Probing of the conduction path in nanoscale by AFM reveals that the grain boundary layer is conductive in CCTO. Therefore, reported giant-dielectric response in CCTO can not be understood by the model of conducting grains surrounded by insulating grain boundaries, which is usually used for the explanation of conventional internal barrier layer capacitors.

DOI： 10.1080/00150190601187500

Web of Science

Scopus

AgNbO<inf>3</inf>: A lead-free material with large polarization and electromechanical response Reviewed

Desheng Fu, Makoto Endo, Hiroki Taniguchi, Tomoyasu Taniyama, Mitsuru Ltoh

Applied Physics Letters Vol. 90 ( 25 ) 2007

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

Polarization measurements reveal that AgNbO3 has an extremely large polarization, which can reach a value of 52 μC/cm2 in polycrystals. Experiments also show that the large internal atom distortion in AgNbO3 is also strongly coupled to the electric field, indicating that high piezoelectric performance can be realized in AgNbO3 system. This finding opens the way to designing a new class of lead-free, high-performance piezoelectric materials based on AgNbO3. ©2007 American Institute of Physics.

DOI： 10.1063/1.2751136

Web of Science

Scopus

High polarization in silver-based oxide

FU Desheng, Endo Makoto, Taniguchi Hiroki, Taniyama Tomoyasu, Itoh Mitsuru

Preprints of Annual Meeting of The Ceramic Society of Japan<br>Preprints of Fall Meeting of The Ceramic Society of Japan Vol. 2007 ( 0 ) page： 503 - 503 2007

Ferroelectricity of SrTiO3 Induced by Oxygen Isotope Exchange

谷口博基

Structure and Bonding 124 page： 89 - 118 2007

その場観測ラマン散乱を用いた強誘電体ガラスの結晶化過程の研究

谷口博基

ニューガラス 84 page： 57 2007

Ferroelectricity of SrTiO<inf>3</inf> induced by oxygen isotope exchange Reviewed

Mitsuru Itoh, Hiroki Taniguchi

Structure and Bonding Vol. 124 page： 89 - 118 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER-VERLAG BERLIN

Typical quantum paraelectric SrTiO3 becomes quantum paraelectric by oxygen isotope exchange. Apparently the change in the Curie temperature Tc is explained by the criteria of the theory for quantum ferro/paraelectrics. Tc for an isotope-exchanged sample depends only on the average mass of oxygen. Ferroelectricity for the oxygen isotope-exchanged SrTiO3 results mainly from the condensation of the Slater-type soft mode. However, an order-disorder component exists in addition to the displacive soft mode component. Raman spectra and NMR results suggest that ferroelectric domains do not develop through the crystal-like normal ferroelectrics. The role of the lattice defect must be elucidated and related to the phase transition mechanism in future works. Oxygen isotope exchange is considered the best way to understand the phase transition mechanism of SrTiO3 because this exchange may not accompany the formation of random fields or defects. © Springer-Verlag Berlin Heidelberg 2007.

DOI： 10.1007/430_2006_046

Web of Science

Scopus

Precursory softening of polar mode in isotope-exchanged paraelectric strontium titanate studied by Raman scattering Reviewed

H. Taniguchi, M. Takesada, M. Itoh, T. Yagi

Ferroelectrics Vol. 337 page： 131 - 138 2006.8

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

Quantum paraelectric SrTiO 3 shows the ferroelectricity by the exchange of 16 O for its isotope 18 O. Raman scattering experiment is performed on the isotopically exchanged SrTi(O 0.32 16 18 O 0.68 ) 3 whose exchange rate is just below the critical exchange rate. Raman spectrum of ferroelectric soft mode in the paraelectric phase clearly indicates local symmetry-breaking induced by the 18 O-exchange. The temperature dependence of the soft mode in SrTi(O 0.32 16 18 O 0.68 ) 3 suggests the occurrence of local ferroelectric region before the onset of the ferroelectric phase. The inhomogeneity of the system induces the inhomogeneous softening of the soft mode in 18 O-exchanged SrTiO3.

DOI： 10.1080/00150190600738196

Web of Science

Scopus

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Papers - TANIGUCHI Hiroki