Phase transitions in SbSI

Abstract

Ferroelectric phase transitions in uniaxial ferroelectrics under high pressures are treated theoretically. It is shown that on the phase transitions lines (p-T diagrams) there can be not only special points at which the thermodynamic expansion coefficient β zeroes with a sign reversal (that is a critical Curie point), but also such special points at which β reaches conditional extremum, for instance, zero value. Behaviour of the ferroelectric in regions of the p-T plane lying near special points of different types is investigated. Basic ferroelectric characteristics and thermodynamic functions are singularly expressed by Δp = p - pk, where pk is the coordinate of the special point.The results of the theoretical analysis are compared with experimental data, obtained when investigating the phase transitions in crystals of SbSI under pressure. It is found that on the phase diagram of SbSI, with p = pk ≈ 5000 bar, there is a special point at which β remaining negative passes through a conditional maximum. The...