Effective size of vacancies in aliovalently doped SrTiO3 perovskites

Abstract

Abstract Point defects like vacancies can have a profound effect on the structure of perovskite ceramics, but the exact mechanisms involved are still unclear. While a few theoretical models exist for some perovskites, none are particularly accurate or at all suited to the impure, doped, or otherwise defective ceramics which abound in commercial devices. A new empirical approach is presented here. A predictive model for the pseudocubic lattice constant of such perovskites, based solely on published ionic radii data, has been developed and adapted as a model for effective tolerance factor. This model shows that the average A-site size generally decreases with increasing vacancy concentration up to [ V ] = 22%, but not as much as would be expected if vacancies were truly zero-dimensional defects. Such vacancies have an effective size due to both bond relaxation and mutual repulsion of coordinating oxygen ions. At compositions corresponding to [ V ] 3 -based perovskites than existing methods and can potentially be expanded to other perovskite systems.