First‐Principles Study on Site Preference of Aluminum Vacancy and Nitrogen Atoms in γ–Alon

Abstract

The disorder in γ–alon is caused by random arrangement of nitrogen atoms and aluminum vacancies. To understand the properties and electronic structure of γ–alon by theoretical methods, the most reasonable structure model is needed. We examined the site preference of nitrogen atoms and aluminum vacancies by first‐principles density functional theory ( DFT ) calculations on Al 24 O 24 N 8 and Al 23 O 27 N 5 . The calculated results for Al 24 O 24 N 8 with the lowest total energy indicated that nitrogen atoms prefer to be far away from each other, rather than in a completely random arrangement. The further investigation on Al 23 O 27 N 5 shows that the aluminum vacancies tend to possess octahedral sites and coordinate only with oxygen atoms. Evaluated by lattice variances ( D a and D θ ) and simulated XRD pattern, the most reasonable structure model of Al 23 O 27 N 5 has little deviation from the experimental results. The calculated bulk modulus of 200.9 GPa in Al 23 O 27 N 5 is slightly lower than the experimental value. The electronic structure reveals that the bonds of Al – N and Al – O have partially covalent and ionic characterization, while the covalent bond strength of Al – N is stronger than that of Al – O . The calculated band gap is 3.99 eV, which is much closer to the experimental 4.56 eV than previous suggestions.