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S. Matsui

Bio: S. Matsui is an academic researcher from Kyoto Institute of Technology. The author has contributed to research in topics: Raman scattering & Phonon. The author has an hindex of 4, co-authored 5 publications receiving 153 citations.

Papers
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Journal ArticleDOI
TL;DR: All the 13 Raman-active phonon modes predicted by group theory, 4A(1)+9E, were observed at low temperature and successfully assigned by a polarized Raman measurement, and drastic spectral changes in the Raman spectra were observed.
Abstract: We have grown BiFeO3 bulk single crystals by a flux method and characterized the phonon spectra in detail by Raman scattering in the temperature range 4?1100?K. All the 13 Raman-active phonon modes predicted by group theory, 4A1+9E, were observed at low temperature and successfully assigned by a polarized Raman measurement. Moreover, drastic spectral changes in the Raman spectra were observed at temperatures 600?700?K and 1000?1100?K. These features are discussed from the viewpoint of phonon coupling with the magnetic ordering and the structural phase transition, respectively.

70 citations

Journal ArticleDOI
TL;DR: YMnO(3) is a multiferroic material in which ferroelectric and antiferromagnetic ordering can coexist and spectra for the high-temperature paraelectric phase showed a sudden change at the Curie temperature T(C)>900 K, suggesting an abrupt structural phase change from the ferroElectric to the paraeLECTric phase.
Abstract: YMnO3 is a multiferroic material in which ferroelectric and antiferromagnetic ordering can coexist. We have studied a YMnO3 bulk crystal in detail by Raman scattering in a wide temperature range of 15–1200 K, with comparison to a previous experiment at room temperature and a theoretical prediction for Raman-active phonon modes. In the low-temperature ferroelectric phase, the observed phonon spectra showed anomalous temperature variation at the Neel temperature, TN~80 K, suggesting a coupling between the spin and phonon systems below TN. Furthermore, spectra for the high-temperature paraelectric phase, reported here for the first time, showed a sudden change at the Curie temperature TC>900 K, suggesting an abrupt structural phase change from the ferroelectric to the paraelectric phase.

64 citations

Journal ArticleDOI
TL;DR: In this paper, Mn-doped BiFeO3 nanoparticles were synthesized up to 10% of Mn composition by a sol-gel process, and the samples showed high crystallinity with no secondary phase up to 2%.
Abstract: BiFeO3 is a multiferroic material showing antiferromagnetic ordering and ferroelectric behavior simultaneously. Here, Mn-doped BiFeO3 nanoparticles were synthesized up to 10% of Mn composition by a sol-gel process. The samples showed high crystallinity with no secondary phase up to 2% of Mn doping. A phonon peak at 1250 cm−1 in undoped BiFeO3 showed anomalous intensity enhancement in the magnetically ordered phase below TN = 643 K due to a spin-phonon coupling. This behavior was less pronounced in the Mn-doped samples, suggesting a suppression of magnetic ordering between Fe spins by Mn doping.

17 citations

01 Jan 2009
TL;DR: In this article, Mn-doped BiFeO3 nanoparticles were synthesized up to 10% of Mn composition by a sol-gel process, and the samples showed high crystallinity with no secondary phase up to 2%.
Abstract: BiFeO3 is a multiferroic material showing antiferromagnetic ordering and ferroelectric behavior simultaneously. Here, Mn-doped BiFeO3 nanoparticles were synthesized up to 10% of Mn composition by a sol-gel process. The samples showed high crystallinity with no secondary phase up to 2% of Mn doping. A phonon peak at 1250 cm−1 in undoped BiFeO3 showed anomalous intensity enhancement in the magnetically ordered phase below TN = 643 K due to a spin-phonon coupling. This behavior was less pronounced in the Mn-doped samples, suggesting a suppression of magnetic ordering between Fe spins by Mn doping.

12 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the crystal structure and phase evolution of NBT and Fe-modified NBT (from 0-2 at.% Fe) using synchrotron x-ray diffraction and Raman spectroscopy, at both ambient and elevated temperatures were reported.
Abstract: Sodium bismuth titanate (NBT) ceramics are among the most promising lead-free materials for piezoelectric applications. This work reports the crystal structure and phase evolution of NBT and Fe-modified NBT (from 0-2 at.% Fe) using synchrotron x-ray diffraction and Raman spectroscopy, at both ambient and elevated temperatures. The crystallographic results are discussed with reference to permittivity and piezoelectric thermal depolarization measurements of the same compositions. Changes in the depolarization temperature due to Fe substitution were detected by Raman spectroscopy and were found to correlate closely with depolarization temperatures obtained from converse piezoelectric coefficient and permittivity measured in situ. The depolarization temperatures obtained from direct piezoelectric coefficient measured ex situ as well as the phase transition temperatures obtained from synchrotron x-ray diffraction were found to be at higher temperatures. The mechanisms underlying the relationship between permittivity and piezoelectric depolarization to structural transitions observed in Raman spectroscopy and x-ray diffraction are discussed.

176 citations

Journal ArticleDOI
TL;DR: A large and reversible, electrically driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material is demonstrated, which is promising for a plethora of applications.
Abstract: We have investigated the nanoscale switching properties of strain-engineered BiFeO3 thin films deposited on LaAlO3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicates that the nearly tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy, we provide clear evidence of ferroelectric switching of the tetragonal phase, but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material, which is promising for a plethora of applications.

150 citations

Journal ArticleDOI
TL;DR: No evidence is found for any systematic variation of the electric or magnetic properties of BiFeO(3) depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grain boundaries.
Abstract: We have synthesized a range of transition-metal-doped BiFeO3 thin films on conducting silicon substrates using a spin-coating technique from metal–organic precursor solutions. Bismuth, iron and transition-metal–organic solutions were mixed in the appropriate ratios to produce 3% transition-metal-doped samples. X-ray diffraction studies show that the samples annealed in a nitrogen atmosphere crystallize in a rhombohedrally distorted BiFeO3 structure with no evidence for any ferromagnetic secondary phase formation. We find evidence for the disappearance of the 404 cm−1 Raman mode for certain dopants indicative of structural distortions. The saturation magnetization of these BiFeO3 films has been found to increase on doping with transition metal ions, reaching a maximum value of 8.5 emu cm−3 for the Cr-doped samples. However, leakage current measurements find that the resistivity of the films typically decreases with transition metal doping. We find no evidence for any systematic variation of the electric or magnetic properties of BiFeO3 depending on the transition metal dopant, suggesting that these properties are determined mainly by extrinsic effects arising from defects or grain boundaries.

134 citations

Journal ArticleDOI
TL;DR: In this article, the phase diagram of lead-free ternary (1 - y)[(1 - x)(Bi0.5Na 0.5)TiO3]-y(K0.6K 0.1)NbO3 (BNT-BKT-KNN) system was studied.
Abstract: In this work, we report the phase diagram of lead-free ternary (1 - y)[(1 - x)(Bi0.5Na0.5) TiO3-x (Bi0.5K0.5)TiO3]-y(K0.5Na0.5)NbO3 (BNT-BKT-KNN) system and study the switching characteristics of the morphotropic phase boundary (MPB). The addition of KNN intrinsically changes the structural nature of the system with the shift of MPB from MPB(I) between ferroelectric rhombohedral and ferroelectric tetragonal phases to MPB(II) between ferroelectric rhombohedral and relaxor pseudocubic phases. As the MPB(I) switches to MPB(II), large piezoelectric response with d(33) similar to 150pC/N that obtained for BNT-0.20BKT near MPB(I) almost disappears. Instead, a significant jump of electric-filed-induced strain S up to 0.32%-0.46% (S-max/E-max = 400-575 pm/V) is achieved near MPB(II) due to the shift of the ferroelectric-relaxor transition temperature TF-R down to room temperature. In this study, giant strain similar to 0.46% occurs in a very narrow region in the BNT-BKT-KNN system with x = 0.20, y = 0.01, which lies on an underlying tricritical triple point of a rhombohedral (R), tetragonal (T), and pseudocubic (Pc) phases. In-situ high-energy X-ray scattering experiments with external electric field reveal an initial electric-field-induced distortion from the Pc structure for the MPB(II) compositions, while those with single R phase shows no such distortion, which suggests that the large strain achieved near the MPB(II) is likely to be induced by the electric-field-induced structure distortion due to its relative instability structure. We believe that the discovery of a compositional line in the pseudo-ternary system, where the strain response is consistently derivable, should be useful for designing high-performance piezoelectric materials in other BNT-based systems by searching MPBs. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795511]

133 citations

Journal ArticleDOI
TL;DR: In this article, the anomalous behavior of the phonon frequencies in orthochromites with magnetic R-ion (Gd and Sm) is compared to those of non-magnetic R-ions (Y, Lu and Eu).
Abstract: Raman study on a select few orthochromites, RCrO$_3$ (R = Y, Lu, Gd, Eu and Sm) shows that the phonon behavior at TN in compounds with magnetic R-ion (Gd and Sm) is remarkably different from that of non-magnetic R-ion (Y, Lu and Eu). While anomalies in most of the observed phonon frequencies in all these compounds may result from the distortion of CrO$_6$ octahedra due to size effect and magnetostriction arising from Cr-ordering, the anomalous behavior of their linewidths observed at TN for the compounds with only magnetic R-ion suggests spin-phonon coupling. The presence of spin-phonon coupling and the anomalies in the low frequency modes related to R-ion motion in orthochromites (R = Gd and Sm) support the suggestion that the coupling between 4f-3d moments play important role in inducing switchable electric polarization.

121 citations