Theoretical and experimental studies were made of O excess defects. A local density functional formalism and a self-consistent discrete variational method were used to determine the energy levels and potentials for a fragment that consisted of 30 to 44 atoms which were embedded in an infinite crystal. Calculations were performed for 3 interstitial-O models, with and without local relaxation. These models included sites which had been proposed on the basis of neutron diffraction and interstitial dimers [O2]q. The dimer charge, q, was found to be consistent with that of normal O ions, and was not equal to -1; as proposed by so-called super-oxide models. Electrostatic energies were used to estimate the relative stabilities of the proposed interstitial structures. The experimentally determined Seebeck coefficient also showed that the charge on interstitial O ions was -2.

Y.Wu, D.E.Ellis, L.Shen, T.O.Mason: Journal of the American Ceramic Society, 1996, 79[6], 1599-604