<title>The structure and electronic properties of Zr and Hf nitrides and oxynitrides</title>

Abstract

The atomic structure, stability and electronic properties of various phases of zirconium and hafnium nitrides in both metallic MN and insulator M₃N₄ forms, and oxynitrides M₂N₂O (M = Zr, Hf) were studied using first-principles plane-wave DFT calculations. The orthorhombic <i>Pnam</i> structure of M₃N₄, which was experimentally observed for zirconium nitride, was found to be the most stable with regard to the rock-salt-type structure often offered for such compounds. The total energy calculations showed that the nitridation of zirconium and hafnium oxides is thermodynamically unfavorable, and the formation of nitrogen vacancies in M₃N₄ converts it into the metallic MN phase. Calculations of the electronic density of states showed that the rock-salt type structure of zirconium and hafnium nitrides leads to their metallic properties in both the MN and M₃N₄ phases, while the orthorhombic structure of the M₃N₄ phase reveals its insulating nature in agreement with the experimental observations. Calculations of the electronic structure of zirconium and hafnium oxynitrides with the cubic Bixbyite-type crystal structure found in a recent experimental study demonstrate that both Zr₂N₂O and Hf₂N₂O are insulators with large energy band gaps.