- 著者
- Ko Jae-Hyeon Lushnikov S. G. Kim Do Han Kojima Seiji Jun Byeong-Eog Hwang Yoon Hwae
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physic (ISSN:00218979)
- 巻号頁・発行日
- vol.104, no.10, pp.104105, 2008-11
- 被引用文献数
- 9 5
Acoustic properties were investigated for four tungsten bronze (TB) uniaxial ferroelectric crystals, i.e., (Sr0.61Ba0.39)5Nb10O30 (SBN61), Cu-doped (K0.5Na0.5)1.0(Sr0.75Ba0.25)4.5Nb10O30 (KNSBN:Cu), K5.80Li3.82Nb10.12O30, and K4.74Li3.07Nb10.44O30 of which the spontaneous polarization is directed along the polar c axis. Large acoustic anisotropy between the two elastic constants C11 and C33 have been observed from all samples. C33 exhibits a significant softening on approaching the diffuse phase transition temperature from high-temperature side while C11 does not show any substantial change in the same temperature range. This softening is accompanied by substantial growth of hypersonic damping, appearance and growth of central peak (CP), and slowing down of the relevant dynamics of CP represented by the reducing half width. All these results indicate that the lattice motions along the c axis couple strongly to the one-component order parameter of the polar nanoregions (PNRs) or precursor polar clusters which form and grow below a certain temperature in the paraelectric phase. The inverse dielectric constant measured along the c axis of SBN61 and KNSBN:Cu can be described by two linear regions divided by a crossover temperature at which the change in the magnitude of dipole moments and the strength of the dipole couplings are expected due to the formation of PNRs. C33 of SBN61 becomes continuously softened upon cooling even when the temperature crosses the Burns temperature TB at which PNRs begin to appear. It may suggest that additional relaxation process other than that of PNRs may exist at high temperatures above TB and couple to the longitudinal acoustic waves propagating along the polar axis. Recent observation of a single-particle relaxation at high temperatures and its transformation into a collective relaxation of PNRs by dielectric spectroscopy [Belous et al., J. Appl. Phys. 102, 014111 (2007)] might be related to the anomalous acoustic behavior of SBN61 observed above TB.
- 著者
- Ko Jae-Hyeon Kojima Seiji Bokov Alexei A. Ye Zuo-Guang
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.91, no.25, pp.252909, 2007-12
- 被引用文献数
- 36 25
The dynamic polar nanoregions (PNRs) which form below the Burns temperature and determine the unique properties of relaxor ferroelectrics were predicted [Tinte et al., Phys. Rev. Lett. 97, 137601 (2006)] to be pinned to the quenched chemically ordered regions (CORs) usually observed in lead-containing relaxors. In Pb[(Mg1/3Nb2/3)0.45Ti0.55]O3 crystal where CORs are known to be absent, we have found the phenomena typically related to the relaxation of dynamic PNRs, namely, the significant Brillouin quasielastic scattering, the softening of the longitudinal acoustic mode, and the deviation from the Curie-Weiss law above the Curie point. This implies that PNRs may appear in crystals without CORs.
- 著者
- Shabbir Ghulam Ko Jae-Hyeon Kojima Seiji
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.86, no.1, pp.012908, 2004-12
- 被引用文献数
- 11 10
High-resolution Brillouin scattering experiments have been performed to investigate the low temperature "aging" effect in lanthanum lead zirconate titanate (PLZT) relaxor ferroelectric ceramics. From the temperature dependence of the frequency shift of longitudinal acoustic mode, an acoustic anomaly was observed at T0~46 K in these ceramics with clear "aging" effect below T0. The results have been discussed in the light of stepwise freezing of the related degrees of freedom causing transition from proper to improper dipole glassy states at T0.