Theoretical study on martensitic-type transformation path from rutile phase to α-PbO₂ phase of TiO₂

The martensitic-type phase transformation paths from the rutile to the α-PbO₂ phase of TiO₂ are studied with linear interpolation and NEB/G-SSNEB methods based on first-principles calculations. Its potential energy surface and the lowest energy path are revealed. Our results indicate that the titanium atoms of the rutile phase shuffle along the 0-11_rut crystal direction to form the α-PbO₂ phase. During the phase transition, the oxygen atoms are dragged by the heavier titanium atoms and then reach their new equilibrium positions. The barrier of phase transition from nudged elastic band theory is about 231 meV, which is qualitatively consistent with previous theoretical calculations from the monoclinic phase to the tetragonal phase for ZrO₂ and HfO₂. Debye model can also be successfully used to predict the pressure and temperature of the phase transformation.