STRUCTURE AND INTERACTION OF IMPURITY VACANCY (MG2+-V-C) DIPOLES IN CRYSTALLINE LIF

Both the spatial and electronic structure of Mg2+, V(c)- and (Mg2+-V(c)-)n centres (n = 1, 4) in a LiF crystal have been calculated by semiempirical techniques of pair potentials and INDO. Crystal polarization was taken into account in a self-consistent way in terms of the Mott-Littleton approach. It is shown that a consistent choice of parametrization of both methods gives rather close values for displacements of ions surrounding the centres under study. The Mg2+ compensation by a cation vacancy located in its nearest surrounding along the [110] axis is found to be most energetically favourable. It is shown that the aggregation of impurity-vacancy dipoles can lead to the formation of a phase with a periodical structure differing from the traditional Suzuki phase.