Heat capacity and T-p phase diagram of Cs_2NH_4GaF_6 elpasolite

摘要

Cs_2NH_4GaF_6 prepared by solid-state reaction exhibits at room temperature a cubic Fm(3-bar)m elpasolite structure with a_0 = 9.167 A. Calorimetric measurements have shown the presence of a first order phase transition at T_0 = 161 K. Pressure dependence of the phase transition temperature has been studied by DTA under pressure. The data are analyzed in the framework of orientational disordering of [NH_4]~+ and [GaF_6]~(3-) ions.