Soft mode behavior in ferroelectrics Sn2P2S6 and Sn2P2Se6 near phase transitions

Abstract The paper presents the results of the microwave dielectric investigations of the semiconductive ferroelectrics Sn2P2S6 and Sn2P2Se6. The dielectric dispersion is caused by the ferroelectric overdamped Buu mode witch softens up to the millimeter range close to Tc. In Sn2P2S6 the soft Bu mode alone is responsible for the high value and the temperature-dependence of ϵ(0). In the incommensurate phase of Sn2P2Se6 the phason causes the main dielectric dispersion at mi crowaves.