Schottky defect enthalpies of alkaline earth oxides

306-312<span style="font-size:14.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:black;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">The Schottky defect formation process in MgO, CaO, SrO, and BaO is investigated using our recently introduced EPPI model3. 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 enthalpies (hfs) are 5.9, 5.8, 4.7 and 1.4 eV respectively for MgO, CaO, SrO, and BaO. The results of cation self diffusion experiments in MgO are reanalyzed to include the effects of impurity-vacancy association reaction. The analysis suggests the previous interpretation of the experimental data to be an oversimplification. Since the binding energy of an impurity - defect complex in MgO could be quite large, the effects of the association reaction on the defect densities are appreciable. On the basis of near complete association of the dominant tetravalent cation impurity, hfs in MgO is found to be 5.8 eV which is in good agreement with the theoretical value of the present work.</span