Theoretical investigation of nitrogen substitution in cubic zirconia

Nitrogen substitution of oxygen ions in cubic zirconia was studied theoretically at density functional level. Nitrogen contents of 12.5 and 3.1% were studied with Zr8O16-mN2 and Zr32O64-mN2 supercells. For both nitrogen concentrations three stoichiometries were considered (m=2, 3, and 4). The stability and electronic structure of local nitrogen-oxygen vacancy configurations was calculated. Several stable defect clusters were found. Their structures depend on nitrogen concentration and stoichiometry. The formation of stable defect clusters explains the experimentally observed nitrogen concentration-dependent increase of activation barriers for anion diffusion in zirconia.