Thermal Properties of Alkaline Earth Oxides

The heat capacities of MgO, CaO, SrO and BaO, reported in part I have been analysed in terms of the frequency spectrum of the lattice with the assumption that the effect of anharmonicity of the lattice may be neglected for T (@D / 3 ) . Following the usual procedure the n-th moments of the frequency spectrum with n = — 3, —2, — 1, 0, 1 to 6 were calculated from the experimental data. From the low frequency expansion the apparent Debye characteristic temperature at 0 ° K , &0 , is calculated to be in good agreement with O 0 (elast.), calculated from elasticity data. Also the limiting values at high temperatures, , and the zero point energy, Ez , have been calculated. A comparison between the heat capacity data, the elastic constants and thermal properties of these oxides and the alkali-halides suggest that the interatomic forces of the alkaline-earth-oxides are rather similar to those of the alkaline fluorides. But no specific divalent character has been detected for these oxides. An appreciable anharmonic effect is present for all oxides.