Structure changes in vacancy-rich titanium monoxide at high pressures and high temperatures

Abstract Powdered samples of TiO0.82, TiO1.04 and TiO1.25 having the cubic rocksalt-type structure with high concentration of vacancies randomly distributed were held at combined conditions of high pressure, ranging from 1 GPa to 8 GPa, and high temperature, ranging from 973 K to 1173 K, and structural changes occurring were investigated by synchrotron radiation diffraction at the conditions and by conventional X-ray diffraction after the samples were brought back to ambient condition. Pressure has been shown to suppress formation of ordered arrangements of vacancies in all the samples and lead to precipitation of a hexagonal δ-Ti3O2 in TiO0.82 and TiO1.04 and precipitation of a corundum-type Ti2O3 in TiO1.25. Irreversible change in the lattice parameter of the remaining rocksalt-type structure has been observed which is due to partial annihilation of vacancies under pressure.