Equations of state and thermal expansion of alkali halides

Abstract

Thermal expansion is the dimensional change which occurs with a change in temperature, revealing something about the dependence on volume of the energies of various interaction processes in solids. Thermal expansion is due to anharmonicity in the potential energy of a crystal. A harmonic crystal would show no thermal expansion; in fact, such a crystal would be mechanically unstable (Barron, 1957). It is thus logical to consider thermal expansion as one of several phenomena withn the general framework of the equations of state which formally and correctly define the concept of anharmonicity.