Splitting of the phase transition in ferroelectric solid solutions Sn2P2(SexS1?x)6 at high pressures

The influence of the temperature and hydrostatic pressure on the forbidden band width and dielectric permittivity of the ferroelectric solid solutions Sn₂P₂(Se_xS_1–x)₆ (x=0.04, 0.20, 0.30) is investigated. A change in the species and splitting of ferroelectric phase transition lines are detected for p = 0.140 and 0.026 GPa, respectively, for the solid solutions Sn₂P₂(Se_0.04S_0.96)₆ and Sn₂P₂(Se_0.20S_{0.80 6}, which is due to the existence of a Lifshits critical point separating the transitions into codimensional and noncodimensional phases on the p, T diagram. Shift coefficients with the pressure of the phase transition temperature are found for the solid solutions investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 28–32, February, 1988.