Electrostatic screening contributions to the vacancy binding energy in doped oxides

Linear Response Theory is used to estimate the relative magnitudes of the electrostatic contributions to the binding energy of an oxygen vacancy to a dopant ion in mixed oxides. The theory is further developed to yield the electrical conductivity activation enthalpy and pre-exponential factor in the ionic conduction regime. Experimentally observed trends in these quantities are not reproduced. The discrepancy is not removed by inclusion of polarization effects associated with the field-induced displacement of the screening cloud around the mobile vacancy or ionized dopant. Both of these are estimated to produce negligible changes. The same applies to the enhancement of the local field at the vacancy due to nearby vacancy—dopant pairs. It is concluded that some other physical mechanism is required to account for the variation in the conductivity activation enthalpy with dopant concentration.