STRUCTURE OF TRANSITION-METAL-OXYGEN-VACANCY PAIR CENTERS

The microscopic structure of the Fe3+-VO and Mn2+-VO pair centers has been considered using the Newman superposition model. This model yields the EPR parameter b20 as a function of transition-metal-ion-oxygen distance d and position. It is found, for the oxide perovskites, that the transition-metal ion moves by a distance Δ=0.1 d=0.2 our lateral oxygens move against the metal ion by 4% or 0.08. This is in agreement with the reduction of the metal ionic radius due to the five-fold coordination. The intrinsic two-center parameter b̄2 needed in the Newman model is based on the uniaxial strain data of MgO and SrTiO3, as well as on the measured spin-Hamiltonian parameter b20 in the tetragonal phase of SrTiO3. The b̄2 parameters obtained also provide information on other centers reported in oxide and fluoride compounds. © 1979 The American Physical Society.