High pressure ferroelastic phase transition inSrTiO3

Abstract

High pressure measurements of the ferroelastic phase transition ofSrTiO3 (Guennou et al 2010 Phys. Rev. B 81 054115) showed a linear pressure dependence of thetransition temperature between the cubic and tetragonal phase. Furthermore, the pressureinduced transition becomes second order while the temperature dependent transition is near atricritical point. The phase transition mechanism is characterized by the elongation and tilt of theTiO6 octahedra in the tetragonal phase, which leads to strongly nonlinear couplingsbetween the structural order parameter, the volume strain and the applied pressure.The phase diagram is derived from the Clausius–Clapeyron relationship and isdirectly related to a pressure dependent Landau potential. The nonlinearities ofthe pressure dependent strains lead to an increase of the fourth order Landaucoefficient with increasing pressure and, hence, to a tricritical–second order crossover.This behaviour is reminiscent of the doping related crossover in isostructuralKMnF3.