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.

Formulae for calculating the electric field produced by microscopic impurities in perovskite-type oxides have been derived. By way of illustration, dipole and monopole impurities in , and were considered. It was found that the lattice polarization leads to a gigantic enhancement of the interaction between dipole impurities that can explain many phenomena in polar lattices.

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