Nitrogen defects in wide band gap oxides: defect equilibria and electronic structure from first principles calculations

Abstract

The nitrogen related defect chemistry and electronic structure of wide band gap oxides are investigated by density functional theory defect calculations of N^q_O, NH^×_O, and as well as and in MgO, CaO, SrO, Al₂O₃, In₂O₃, Sc₂O₃, Y₂O₃, La₂O₃, TiO₂, SnO₂, ZrO₂, BaZrO₃, and SrZrO₃. The N^q_O acceptor level is found to be deep and the binding energy of NH^×_O with respect to and is found to be significantly negative, i.e. binding, in all of the investigated oxides. The defect structure of the oxides was found to be remarkably similar under reducing and nitriding conditions (1 bar N₂, 1 bar H₂ and 1 × 10⁻⁷ bar H₂O): NH^×_O predominates at low temperatures and predominates at higher temperatures (>900 K for most of the oxides). Furthermore, we evaluate how the defect structure is affected by non-equilibrium conditions such as doping and quenching. In terms of electronic structure, is found to introduce isolated N-2p states within the band gap, while the N-2p states of NH^×_O are shifted towards, or overlap with the VBM. Finally, we assess the effect of nitrogen incorporation on the proton conducting properties of oxides and comment on their corrosion resistance in nitriding atmospheres in light of the calculated defect structures.