Defect Structure, Ionic Conductivity, and Diffusion in Calcia‐Stabilized Zirconia

Abstract

A quantitative theoretical model which accounts for the variations of ionic conductivity of calcia‐stabilized zirconia, , with oxygen vacancy concentration, , and temperature, , has been developed based on the consideration of effective anion‐site coordination of effectively negatively charged calcium ion, Ca^2′. The theory extends the conventional concept of dopant‐defect complexes (or associates) and demonstrates that ionic conduction in this system proceeds by a multimode mechanism through and between different degrees of dopant‐defect associates. The primary mechanism is oxygen transport through the channel of onefold effectively Ca^2′ coordinated anion sublattice, that is, oxygen vacancy Vo^2ċ transport inside the onefold bonded (Ca^2′‒Vo^2ċ) defect complex. The theory subsequently predicts the occurrence of a rather sharp maximum of ionic conductivity at oxygen vacancy concentration and reproduces the experimental isothermal log σ vs. curves reported by various investigators quite satisfactorily. Accordingly, numbers of parameters which characterize the defect structure, the ionic conduction, and the diffusion process in this system are derived from the curve‐fitting procedure of the theoretical expression for ionic conductivity with experimental ones.