Thermal Properties of Alcaline-Earth-Oxides / III. Analysis of Anharmonic Effects

Abstract

Experimental heat capacity data for the alcaline-earth-oxides have been used to analyse by a new method the high temperature thermodynamic properties of these crystals in terms of quasi-harmonic and explicit anharmonic contributions. The explicit anharmonic contribution ΔC is consistent with theoretical predictions; ΔC is proportional to T in a first order approximation. The factor of anharmonicity A is negative for MgO, A = (-0.4 + 0.4) · 10^-5 K^-1 , for SrO A= (-2.8±1) · 10^-5 K^-1 and for BaO A=(-3.9±1) ·10^-5 K^-1 , but positive for CaO A = (2.3 ± 1.2) · 10^-5 K^-1. Comparison with the results of analysis of the anharmonic effects in the alcaline-halides shows that the alcaline-earth-oxides may be treated by the same models valuable for the alcaline-halides. The results suggest that the type of anharmonic forces is determined in the alcaline-halides as well as in the alcaline-earth-oxides primarily by the cation of the salt.