Schottky defect enthalpies of alkaline earth oxides

The Schottky defect formation process in MgO, CaO, SrO, and BaO is investig ated using our recently introduced EPPI model.(3) We find that inclusion of quadrupolar interactions makes a substantial contribution to the formation energy by values ranging from 1.2 eV to 2.9 eV. The EPPI values of the ent halpies (h(s)(f)) are 5.9 ,5.8 ,4.7 and 1.4 eV respectively for MgO, CaO, S rO, and BaO. The results of cation self diffusion experiments in MgO are re analyzed to include the effects of impurity-vacancy association reaction. T he analysis suggests the previous interpretation of the experimental data t o be an oversimplification. Since the binding energy of an impurity - defec t complex in MgO could be quite large, the effects of the association react ion on the defect densities are appreciable. On the basis of near complete association of the dominant tetravalent cation impurity, h(s)(f) in MgO is found to be 5.8 eV which is in good agreement with the theoretical value of the present work.