Hehlen B, Al-Sabbagh M, Al-Zein A, Hlinka J
Laboratoire Charles Coulomb (L2C) UMR CNRS 2251, University of Montpellier, 34095 Montpellier, France.
European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France, and Physics Department, Faculty of Science, Beirut Arab University (BAU), Beirut, Lebanon.
Phys Rev Lett. 2016 Oct 7;117(15):155501. doi: 10.1103/PhysRevLett.117.155501.
The fluctuations of electric polarization in a disordered ferroelectric substance, relaxor crystal PbMg_{1/3}Nb_{2/3}O_{3} (PMN), were studied using a nonlinear inelastic light-scattering technique, hyper-Raman scattering, within a 5-100 cm^{-1} spectral interval and in a broad temperature range from 20 to 900 K. The split ferroelectric mode reveals a local anisotropy of up to about 400 K. Spectral anomalies observed at higher temperatures are explained as due to avoided crossing of the single primary polar soft mode with a temperature-independent, nonpolar spectral feature near 45 cm^{-1}, known from Raman scattering. The temperature changes of the vibrational modes involved in the measured fluctuation spectra of PMN were captured in a simple model that accounts for the temperature dependence of the dielectric permittivity as well. The observed slowing down of the relaxational dynamics directly correlates with the huge increase of the dielectric permittivity.
利用非线性非弹性光散射技术——超拉曼散射，在5 - 100 cm⁻¹光谱区间以及20至900 K的宽温度范围内，研究了无序铁电体、弛豫晶体PbMg₁/₃Nb₂/₃O₃（PMN）中的电极化涨落。分裂的铁电模式显示出高达约400 K的局部各向异性。在较高温度下观察到的光谱异常被解释为，是由于单一的初级极性软模与拉曼散射中已知的、在45 cm⁻¹附近与温度无关的非极性光谱特征的避免交叉所致。在一个简单模型中捕捉到了PMN测量涨落光谱中涉及的振动模式的温度变化，该模型也考虑了介电常数的温度依赖性。观察到的弛豫动力学减慢与介电常数的大幅增加直接相关。
