Oxygen Surface Exchange in Mixed Ionic Electronic Conductors: Application to La0.5Sr0.5Fe0.8Ga0.2 O 3 − δ

We propose an oxygen surface exchange model in which the effect of vacancies at the gas-mixed ionic electronic conductor interface are included and apply the model to isotope exchange, oxygen permeability, and electrical conductivity relaxation. We deduce relationships between the surface-exchange coefficients associated with these phenomena and extend the treatment of the conductivity relaxation to large changes in oxygen partial pressure, where the commonly used assumption of first order reaction rate breaks down We apply the model to interpret the permeation and electrical conductivity relaxation measurements in La 0.5 Sr 0.5 Fe 0.8 Ga 0.2 O 3-δ . Transport in the material is almost completely surface limited, and data were interpreted in terms of a single surface-exchange coefficient.