Brillouin scattering at the phase transitions in some ferroelectrics

This paper reviews the experimental studies of acoustic anomalies at the phase transition in some ferroelectrics. Primary emphasis is upon possibilities of Brillouin light scattering in revealing of some new and unusual features occurring at “usual” phase transitions. We shall consider in detail a modification of typical anomalies in the behavior of sound velocity and attenuation due to existence of specific phenomena in the crystals under investigation. The specialities are determined by belonging of the TGS crystals to a group of uniaxial ferroelectrics. In the case of TSCC and Li2Ge7O15 the situation is more complicated because we have to attribute these two formally uniaxial ferroelectrics to a new class of weak ferroelectrics. At last, in Gd2(MoO4)3 there is an unusual broad central peak correlating with a pronounced acoustic anomaly. Taking into account individual features of these crystals one can explain their very unusual behavior in the framework of the Landau phase transition theory.