Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8573, Japan.
Department of Physics, Begum Rokeya University, Rangpur, Rangpur, 5400, Bangladesh.
Sci Rep. 2017 Mar 16;7:44448. doi: 10.1038/srep44448.
In relaxor ferroelectrics, the role of randomly orientated polar nanoregions (PNRs) with weak random fields (RFs) is one of the most puzzling issues of materials science. The relaxation time of polarization fluctuations of PNRs, which manifests themselves as a central peak (CP) in inelastic light scattering, is the important physical quantity to understand the dynamics of PNRs. Here, the angular and temperature dependences of depolarized and polarized CPs in 0.44Pb(MgNb)O-0.56PbTiO single crystals with weak RFs have been studied by Raman and Brillouin scattering, respectively. The CPs observed in Raman scattering show the very clear angular dependence which is consistent with the local tetragonal symmetry. It is different from the well-known local rhombohedral symmetry with strong RFs for Pb(MgNb)O. In Brillouin scattering, depolarized and polarized CPs show two relaxation processes corresponding to transverse and longitudinal fluctuations of PNRs. The remarkable slowing down towards the Curie temperature was observed for transverse fluctuations in local tetragonal symmetry.
在弛豫铁电体中，具有弱随机场 (RF) 的随机取向的极性纳米区 (PNR) 的作用是材料科学中最令人困惑的问题之一。PNR 极化涨落的弛豫时间，表现为非弹性光散射中的中心峰 (CP)，是理解 PNR 动力学的重要物理量。在这里，通过拉曼和布里渊散射分别研究了具有弱 RF 的 0.44Pb(MgNb)O-0.56PbTiO 单晶体中去极化和极化 CP 的角度和温度依赖性。拉曼散射中观察到的 CP 表现出非常清晰的角度依赖性，与局部四方对称一致。这与具有强 RF 的 Pb(MgNb)O 的众所周知的局部菱方对称不同。在布里渊散射中，去极化和极化 CP 显示出对应于 PNR 横向和纵向涨落的两个弛豫过程。在局部四方对称中，横向涨落表现出明显的朝居里温度减慢的趋势。
