title: Relaxor Ferroelectrics: Back to the Single-Soft-Mode Picture.
abstract: 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.
authors: Laboratoire Charles Coulomb (L2C) UMR CNRS 2251, University of Montpellier, 34095 Montpellier, France.
authors: B
authors: B
authors: Hehlen
authors: Laboratoire Charles Coulomb (L2C) UMR CNRS 2251, University of Montpellier, 34095 Montpellier, France.
authors: M
authors: M
authors: Al-Sabbagh
authors: European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France, and Physics Department, Faculty of Science, Beirut Arab University (BAU), Beirut, Lebanon.
authors: A
authors: A
authors: Al-Zein
authors: Institute of Physics, The Czech Academy of Sciences, Na Slovance 2, 18221 Praha 8, Czech Republic.
authors: J
authors: J
authors: Hlinka