Simulations of some simple localised defects in alkali-doped alkaline-earth fluorides

Abstract

Using a simulation code for defective ionic crystals, the geometrical structure and the formation energies of some simple defects are calculated for alkali- (Li-, Na-, K-, Rb-) doped alkaline-earth fluorides (CaF2, SrF2); their migration, clustering and reorientation tendencies are also estimated. The alkali-interstitial-alkali-substitutional pair and the fluorine-vacancy-alkali-substitutional pair are the most probable defects. The ion-size effects of the alkali ions are discussed. The authors highlight the chief weakness of these defect models: the poor knowledge of the short-range interactions in these 'mixed' materials (alkali fluoride, alkaline-earth fluorides).