Studies on phase transformation of alkali halide crystals under the effect of high temperature

Abstract

We present an analysis of the phase transformations from solid (NaCl structure) to solid (ZnS structure), and solid (crystalline) to liquid (molten) state for sixteen alkali halides. The calculations are performed using an interionic potential model which includes the overlap repulsive interactions upto second neighbours and the van der Waals dipole-dipole and dipole-quadrupole interactions. The relative stability of NaCl and ZnS structure is predicted correctly. Values of temperatures for NaCl to ZnS structural transitions are found to be much higher than the corresponding values of melting temperatures. The nearest neighbour interionic separations in alkali halides considered with ZnS structure are found to be significantly different from the molten state values. Values of melting temperatures calculated using molten state interionic separations present close agreement with experimental data.