A theoretical study of the formation and aggregation of vacancy-impurity dipoles in divalently doped alkali halide crystals

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Abstract
Computer simulation techniques based on generalized Mott-Littleton methods have been used to investigate defect structures in systems resulting from the incorporation of Mn2 +, Cd2+ and Pb2+ ions into NaCl, KC1 and KBr crystals. Two-body interionic potentials based on the simple shell model were used in the calculations. The (110) nearest-neighbour (n.n.) and (200) next-nearest neighbour (n.n.n.) simple impurity-vacancy dipoles were found to be of comparable stability, although definite trends with ion size are evident, whereas the (211) complex invariably is found to be less stable. The additional binding energies which arise when the n.n. and n.n.n. dipoles aggregate into a variety of dimers, trimers and tetramers have been calculated, as has the stability of the Suzuki phases. In the present work the results are compared with available experimental data and possible pathways for the formation of the Suzuki phase are discussed.