Ferroelectricity and Polarons in Sn2P2S6 Crystals

For Sn2P2S6 ferroelectric-semiconductor the relaxation processes at low temperatures in the ferroelectric phase were investigated by low frequency dielectric and Raman spectroscopies. Observed anomalies in dielectric losses and their change under illumination together with lattice anharmonicity appearance in Raman spectral bands shape are compared with previous data on photo-and thermoluminescence. The experimental data are analyzed with consideration of local three-well potential in ground state and explained by creation and annihilation of small hole and electron polarons with participation of tin vacancies acceptor and sulfur vacancies donor in gap energy states.