The stability and structural properties of titanium oxynitrides, ${\text{TiN}}_{1-x}{\text{O}}_x$, of different compositions are theoretically analyzed by means of first-principles periodic density-functional calculations. We show that at $x=0.55–0.6$ there is a change in the preferred structure from that of NaCl type to the $\alpha \text{-TiO}$ arrangement. For the NaCl-type structure the cell volume increases with $x$ while it decreases with $x$ for the $\alpha \text{-TiO}$ structure. The bulk moduli are always much larger for NaCl-type structures than for $\alpha \text{-TiO}$ and they decrease as the amount of O increases, moving from 280 GPa for TiN to 226 GPa for TiO (NaCl-type structure) or 197 GPa for $\alpha \text{-TiO}$. Changes in the electronic structure with the composition are also considered. In general we found that in the two types of structure (NaCl and $\alpha \text{-TiO}$), both the band gap and the ionic character increase with the O concentration.

• Received 7 June 2009

DOI:https://doi.org/10.1103/PhysRevB.80.184112