To identify the origin of the experimentally observed nitrogen over- and understoichiometry in TiAlN thin films, various point defect configurations were studied by ab initio calculations in terms of formation energies, equilibrium volume and elastic moduli. From formation energies and comparison to existing experimental equilibrium volume and elasticity data, it was shown that nitrogen vacancies and metal vacancies were responsible for nitrogen understoichiometry and overstoichiometry, respectively. Irrespective of the type of vacancies, the bulk modulus was decreased by approximately 7% as the nitrogen concentration was increased or decreased by 3at%.

Origin of the Nitrogen Over- and Understoichiometry in Ti0.5Al0.5N Thin Films. M.Baben, L.Raumann, D.Music, J.M.Schneider: Journal of Physics - Condensed Matter, 2012, 24[15], 155401