Structural phase transition and mechanical properties of TiO2 under high pressure


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A systematic examination of structural phase transitions and mechanical properties for TiO2 under high pressure has been performed by using first-principles calculations. First, we show that the orthorhombic Pca21 structure becomes stabilize at certain pressure and temperature, whereas the cubic fluorite and pyrite structures are not energetically viable in the whole pressure range of 0–200 GPa. These findings support that the experimentally assumed cubic TiO2 should be the Pca21-type TiO2. Secondly, our calculated equations of state for various TiO2 polymorphs are consistent with previous experimental and theoretical results. The only exception is the baddeleyite phase for which we find a significantly lower bulk modulus of 149 GPa than the measured value 290–304 GPa. Finally, our calculations reveal that the recently synthesized Fe2P-type TiO2 exhibits semiconducting features and has the potential to be a superhard material under ultrahigh pressure. It is shown that the high pressure could open a valid avenue for new hard or superhard materials.