Nonmetal sublattice population induced defect structure in transition metal aluminum oxynitrides

The influence of oxygen concentration on the structure and mechanical properties of V0.5Al0.5OxN1−x thin films (0 ≤ x ≤ 0.8) was investigated. The unexpected experimental lattice parameter decrease with increasing oxygen concentration can be understood based on ab initio data: the oxygen incorporation induced formation of metal vacancies reduces the equilibrium volume and stabilizes the metastable solid solutions. Charge balancing is identified as the underlying physical mechanism by Bader decomposition analysis. Hence, property predictions for these oxynitrides are only meaningful if the defect structure is described.