Thermal Properties of Alcaline-Earth-Oxides

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 AC is consistent with theoretical predict ions ; AC is proportional to T in a first order approximation. The factor of anharmonicity A is negative for M g O A — ( — 0.4 + 0.4) I O " 5 K 1 , for SrO A= ( 2 . 8 ± 1 ) I O 5 K 1 and for BaO ^ = ( 3 . 9 ± l ) I O " « K 1 , but positive for CaO A = (2.3 ± 1.2) • 1 0 ~ 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.