Theoretical study of superionicSrCl2below the critical temperature by a simple model

Here we study theoretically the superionic fluorite ${\mathrm{SrCl}}_2$ below the critical temperature $T_c$ assuming Frenkel defects with cube-center interstitials. With quite simplified assumptions regarding the vibrational energy and polarization mechanism reasonable agreement with experimental values is obtained. The defect concentration and lattice constant at high temperatures are derived by minimizing the free energy. The calculation illustrates that the defect concentration is about 1.5% near $T_c$, and that there is a strong attractive anion-anion interaction. These features are consistent with other theoretical and experimental works.