Mechanical properties and structural identifications of cubic TiO2

First- principles calculations on the mechanical properties and structural identifications of the fluorite- and pyrite- TiO2 under high pressure have systematically been performed by the plane- wave basis pseudopotential method. Our calculated bulk modulus ( 272 - 324 GPa ), shear modulus ( 97 - 128 GPa ), elastic constant C-44 ( 40 - 73 GPa ), and theoretical hardness ( 13 GPa ) of the fluorite- TiO2 show that it cannot be regarded as a potential candidate of superhard materials. Our results indicate that the differences of mechanical properties between the fluorite- and pyrite- TiO2 are very small, which are at odds with the previous conclusions. In addition, we find that c- TiO2 in the previous experiment is closer to the fluorite phase by analyzing the high- pressure behaviors of both cubic phases.