Stable Ti$_9$O$_{10}$ nanophase grown from nonstoichiometric titanium monoxide TiO$_y$ nanopowder

A new stable Ti$_9$O$_{10}$ nanophase (sp. gr. Immm) has been detected by X-ray diffraction (XRD) after high energy ball milling and long-term vacuum annealing of nanocrystalline powder of nonstoichiometric disordered and ordered titanium monoxide TiO$_y$ with B1 structure (sp. gr. Fm$\bar3$m). With the help of XRD data, the unit cell of the Ti$_9$O$_{10}$ nanophase as well as the distribution of atoms and structural vacancies in the titanium and oxygen sublattices of this phase have been established. The crystal structure of Ti$_9$O$_{10}$ is derived from that of TiO$_y$ by (a) a migration of the vacancies to the specific crystallographic planes of B1 structure and (b) by orthorhombic distortions. The DFT calculations of the full energy of the coarsecrystalline phases TiO$_y$ and Ti$_9$O$_{10}$ revealed that the bulk ordered phase Ti$_9$O$_{10}$ is not preferable in comparison with the bulk disordered cubic phase TiO$_y$ with the same content of vacancies in the sublattices, so, it is the nanostate that causes the formation of Ti$_9$O$_{10}$.