A theoretical study of the energies of solution, association, and migration for univalent substitutional anion impurities in alkali metal chloride crystals

Theoretical calculations have been made of the energy change accompanying the substitution of a univalent anion, F − , Br − , or I − , into crystals of the alkali metal chlorides LiCl, NaCl, KCl, and RbCl. Association energies for the formation of nearest neighbour (nn) or next nn complexes with a vacancy in the anion sub-lattice and the activation energies for the four basic kinds of single vacancy jumps have also been calculated. The results of these calculations are discussed with respect to ion size and polarization effects and their relation to the activation energy (E′) for the diffusion of a univalent impurity in the host crystals. The availability of experimental values of E′ for some systems permits an assessment of the contribution to E′ from the temperature dependence of the correlation factor and from vacancy pair diffusion.