A central peak in light scattering from the relaxor-type ferroelectric Na1/2Bi1/2TiO3

A complex perovskite-type single crystal Na1/2Bi1/2TiO3 (NBT) has been studied by Raman scattering. A broad central component has been revealed to analyze the temperature dependence of its intensity and width for the first time. The central component has features of a relaxation mode with the highest intensity in the intertransition region, so it arises from a critical light scattering on fluctuations of two coupled order parameters. The correlations between the central component behaviour, acoustic anomalies and dielectric response as well as their relation to a model with competing interactions are discussed. It is suggested that the broad central peak component in light scattering is characteristic of the relaxer-type ferroelectrics with a sequence of phase transformation irrespective of whether transitions are really observed as in NET or whether transitions are frustrated under normal conditions as in PbMg1/3Nb2/3O3 (PMN). (C) 2001 Elsevier Science B.V. All rights reserved.