Analysis of thermal expansion for alkali halide crystals using the isobaric equation of state

Abstract

The isobaric equation of state is used to study the thermal expansion for 16 alkali halide crystals with the NaCl structure at temperatures starting from the static lattice up to their melting temperatures. The calculations are performed using two models, viz. (i) the simple Born-Mayer model and (ii) the model based on Harrison's overlap repulsive potential form which takes into account the interactions up to second neighbours and the van der Waals dipole-dipole and dipole-quadrupole interactions. It is found that the second model gives better agreement with the experimental data for thermal expansion up to the melting temperatures for all the crystals under study. The melting temperatures in each case are found to correspond to nearly a 4 per cent expansion of the nearest neighbour cation-anion distances relative to the room temperature values. This prediction is consistent with the results obtained from computer simulation studies.