On the ferroelastic phase transition in LiKSO₄: Brillouin scattering studies from 140 to 300 K and Landau theory modelling

Abstract

The authors report on the results of Brillouin scattering studies of single crystals of ferroelastic LiKSO2 in the range of temperatures from 140 to 300 K. They have measured all the nonzero second-order elastic constants and found them to be essentially temperature-independent except for c66. The interesting hysteretic temperature dependence of c66, its incomplete softening at the transition temperature and other physical properties of LiKSO4 previously reported have motivated them to re-examine and extend the theoretical models adopted earlier. A Landau expansion of the free-energy involved strain components including spontaneous strain, polarisation and both order parameters for the two neighbouring transitions around 190 and 250 K. As a result of this analysis they have obtained good qualitative agreement with the reported experimental data.