Effect of high pressures and high temperatures on the structure of nanostructured titanium monoxide

The structure of nanostructured titanium monoxide TiO$_{0.98}$ containing structural vacancies in two sublattices simultaneously has been modified via thermobaric annealing. Analysis of the experimental data on thermobaric synthesis of nanostructured TiO$_{0.98}$ with cubic $B1$ type structure at temperatures $573$–$2273$ K and pressure $6$ GPa revealed that a transition from the cubic $B1$ (sp. gr. $Fm\overline{3}m$) phase to the trigonal Ti$_2$O$_3$ (sp. gr. $R\overline{3}c$) phase takes place in the nanostructured monoxide as a result of high pressures and high temperatures. The first-principle calculations of the cohesive energy and electronic structure show that the trigonal phase with space group $R\overline{3}c$ is energetically favorable compared to the cubic phase of the same composition TiO$_{3/2}$ and the orthorhombic ordered Ti$_2$O$_3$ (sp. gr. $Immm$) phase.