High-Temperature Thermal Expansion of Rocksalt

Abstract

It is shown that the temperature dependence of the thermal expansion of NaCl, at temperatures above 500°C, can be related to the concentration of thermally generated Schottky defects. The thermal expansion is considered to consist of two terms; a "normal" contribution and an "anomalous" part; the latter includes the effect of vacancies upon the potential of the lattice in their immediate vicinity. The magnitude of the "anomalous" contribution increases exponentially with temperature with an activation energy consistent with that deduced from ionic conductivity studies.