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RISS 인기검색어
- 검색키워드
- 저자 : SeijiKojima (검색결과 3 건)
- 무료
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- 유료
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Brillouin Scattering Study of Strontium Barium Niobate at Low Temperatures
Jae-HyeonKo,SeijiKojima 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.41 No.2
Many tungsten-bronze ferroelectric crystals are known to exhibit transverse dielectric anomalies along the direction perpendicular to the uniaxial polar c-axis below 150 K, which was conrmed by the present dielectric investigation. Brillouin spectra of uniaxial ferroelectric strontium barium niobate, (Sr0:61Ba0:39)5Nb10O30 (SBN61) have been examined at low temperatures below the diffuse phase transition point at 345 K. Special attention has been paid to the possible existence of a low-temperature structural phase transition from tetragonal to monoclinic symmetry. The temperature dependence of the frequencies of the acoustic waves seems to be governed by the Debye anharmonic eect without showing any coupling. The acoustic properties probed by Brillouin scattering combined with dielectric and pyroelectric results do not reveal any appreciable structural changes below 150 K, in contrast to the previous suggestion of a low-temperature phase transition from tetragonal to monoclinic phase. In addition, the present study reveals the existence of a central peak over a wide temperature range in SBN61. Major ndings about the behavior of the central peak will be brie y presented.
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Raman Scattering Study of Relaxor Ferroelectric Pb(Sc1/2Nb1/2)O3 Crystals
Kohei Suzuki,SeijiKojima,Muhtar Ahart,Yonghong Bing,Zuo-Guang Ye 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.8
The effects of B-site ordering and vacancies were studied in the relaxor ferroelectric Pb(Sc1/2Nb1/2)O3 (PSN) family by using Raman scattering spectroscopy. Differences with Raman spectra and the depolarization ratios were clearly observed among B-site disordered PSN (PSN-D),B-site ordered with lead/oxygen vacancies PSN (PSN-OV ), and 0.7Pb(Sc1/2Nb1/2)O3-0.3PbTiO3(PSN-30PT) single crystals. The temperature dependence of the depolarization ratio of PSN-30PT was also studied to clarify the ferroelectric phase transitions and the polarization fluctuations in the polar nanoregions.
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Raman Scattering Study of A- and B-site Substitutions in Ferroelectric Bi4Ti3O12
AnwarHushur,Jae-HyeonKo,SeijiKojima,SangSeobLee,Min-SuJang 한국물리학회 2002 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.41 No.5
Modied bismuth titanate ceramics, LaxBi4-xTi3O12(LBT) (x=0.0, 0.2, 0.4, and 0.8) and Bi4Ti3-yNbyO12 (NBT) (y=0.0, 0.1, 0.2, 0.3, and 0.4), with bismuth-layered perovskite structures were studied using Raman scattering. With an increase in the La content in LaxBi4-xTi3O12, the lowest soft mode around 30 cm-1 shows a remarkable softening at room temperature. Bi displacements in a pseudo-perovskite layer seem to play a major role in the softening of this mode. However, the rigid-layer mode at 62 cm-1 does not show any remarkable change with La substitution. These facts re ect that the La ions occupy the Bi sites in the pseudo-perovskite units (the A site in the pseudo-perovskite layer) instead of [Bi2O2]2+ layers, at least in the examined concentration range of x less than 0.9. Except for the mode at 850 cm-1, the Raman spectra of Bi4Ti3-yNbyO12 ceramics re not sensitive to the Nb substitution. The Ag mode around 850 cm-1 becomes a little soft while its linewidth increases markedly with increasing Nb concentration. This may indicate that the Ti sites at the centers of the oxygen octahedra (the B site in the pseudo-perovskite layer) are occupied by Nb ions and that the structural disorder at the Ti sites due to the charge imbalance and the different ionic radii may cause the distribution of the force constant responsible for this symmetric stretching mode.
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