An atomistic calculation of extended planar defects in ionic crystals Application to stacking faults in the alkali halides

Abstract

A method for calculating the energy and structure of extended planar defects in ionic crystals is described. The shell model is used and all the lattice sums are carried out over planes, periodic in two dimensions. The crystal block structure necessary for calculating defects on charged planes is described. The method is applied to a study of stacking faults on the (100), (110) and (111) planes of the lithium, sodium, potassium and rubidium halides with the rock-salt structure. Results are obtained that are qualitatively similar to those obtained earlier by Fontaine (1968). The (110) fault is particularly interesting since it is speculated that dislocations dissociate on this plane. Our calculated values are substantially higher than those reported by Fontaine for this fault, making dissociation less likely, but any calculation for an infinite stacking fault cannot rule out the possibility.