Baric dependence of the fundamental absorption edge in the region of phase transitions of Sn2P2S6-type intrinsic ferroelectrics

The energy position of the fundamental absorption edge in the neighborhood of phase transitions in Sn₂P₂S₆ and (Pb_0.1Sn_0.9)₂P₂S₆ ferroelectric crystals is studied as a function of the temperature and baric dependence on the basis of direct measurements of the isoabsorption relations. Thep, T phase diagram of Sn₂P₂S₆ crystals is constructed. the temperature-dependent variation of the band gap in those crystals is due mainly to electron-phonon interaction. Uzhgorod State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 82–85, August, 1997.