The ion-channelling spectra of as-grown crystals were studied by using a 2MeV 4He+ analyzing beam. It was found that the measured minimum back-scattering yields could not be explained in terms of a model which was based upon non-interacting point defects whose concentrations were estimated from the deviation from ideal stoichiometry. An alternative explanation was suggested which included extended defects that were formed by vacancy clustering, and the formation of dislocations in order to accommodate large deviations from stoichiometry.

M.V.Yakushev, H.Neumann, R.D.Tomlinson: Crystal Research and Technology, 1995, 30[1], 121-8