Special features of atomic vacancies in oxides of the perovskite family have been studied within the framework of the Green function method. It has been shown that, in accordance with experiments, the oxygen vacancy has both shallow and comparatively deep levels corresponding to different charge states. The single-charged oxygen vacancy has a deep level and, hence, it could be a good trap for electrons. We shall show that, owing to interaction with the lattice polarization, an electron is captured by one of the neighbours to the vacancy ions. As a result the single-charged oxygen vacancy proves to be a dipole centre. Peculiarities in the optical absorption spectra connected with the single-charged oxygen vacancy are discussed.

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In terms of the multiple-scattering theory using the cluster version of the local coherent-potential approximation the electronic energy structures of both stoichiometric and non-stoichiometric cubic boron nitride have been calculated. It was found that vacancies induced in the sublattice of nitrogen in boron nitride resulted in a marked change in the nitrogen p-band, in a noticeable low-energy shift of the total density of electron states of the valence band and in the appearance of additional acceptor energy levels in the region of forbidden energies. The latter explains the twofold increase in the electrical conductivity of non-stoichiometric boron nitride in comparison with stoichiometric boron nitride found experimentally and calculated in the present work. The calculated partial and total densities of electron states of boron nitride have been used to explain the form of its experimental x-ray emission and x-ray photoelectron spectra.