Calculation of the formation entropy of vacancies due to anharmonic effects

Abstract

The free energy due to the local dilatation created by a vacancy has been calculated from macroscopic parameters for rare-gas solids, alkali halides with NaCl structure, and metals. From its dependence on temperature the corresponding entropy of formation has been obtained. For each of the three categories the resulting values are, respectively, in the region 2-3, 10, 1-2 (in k units) which is the region of the published experimental values. This shows that anharmonicity (i.e., the thermal variation of the bulk modulus) gives a very important contribution to the total entropy of formation.