Cubic ordered modification of titanium monoxide with structural vacancies on metal and nonmetal sublattices: electronic structure and stability

The electronic structure of the recently suggested cubic ordered phase Ti$_{5}$O$_{5(cub.)}$ of titanium monoxide has been studied by means of accurate first-principles calculations within the density functional theory with pseudo-potential approach based on the plane wave basis. It was found that Ti$_{5}$O$_{5(cub.)}$ is the only phase of titanium monoxide without $p$-$d$ gap in the occupied states region. In this sense, calculated DOS's of the cubic modification is closer to the experimental electronic spectrum of the ordered titanium monoxide than that of the well studied ordered monoclinic modification Ti$_{5}$O$_{5(mon.)}$. The enthalpy of formation of Ti$_{5}$O$_{5(cub.)}$ is higher than the enthalpy of Ti$_{5}$O$_{5(mon.)}$ but is less than that of the disordered cubic phase TiO$_{1.0}$.