The segregation of calcium ions at the surface of magnesium oxide: theory and calculation

Atomistic simulation methods have been used to calculate the energetics of substitution and segregation of calcium ions near and at the {001} and {110}¦ surfaces of magnesium oxide at thermal equilibrium. Defect clusters and complete planes of segregating ions have been considered, thereby including impurity-impurity interaction terms. Calculated enthalpies of segregation of –0.42 and –0.78 eV, derived from different interatomic potentials, are in good agreement with the experimental heat of segregation of –0.78±0.22 eV reported recently by Wynblatt and McCune. A simple statistical mechanical theory leads to an Arrhenius expression for large crystals and the deviation from this behaviour expected in microcrystallites.