| Popis: |
Theoretical methods, based on Mott-Littleton techniques are used to investigate the defect structures of alkali-halide crystals doped with divalent ions. The systems studied are those having Mg 2+ , Ca 2+ , Sr 2+ and Ba 2+ as impurity ions in NaCl, KCl and KBr crystals. Our calculations find comparable stability of the (110) nearest-neighbour and (200) next-nearest-neighbour complexes whereas the (211) complex is found to be less stable. Significant trends in the variation of binding energy with dopant ion radius are predicted. We also consider the activation energies for the w 1 , w 2 , w 3 and w 4 type jumps which occur in the vicinity of the impurity ion. The results are, where possible, compared with experimentally determined defect energies and their implications in diffusion processes of M 2+ impurities in the alkali halides are discussed. |
