X-ray study of the transitions among the rutile, α-PbO2 and baddeleyite phases of TiO2 at high pressure and high temperature

Abstract

The phase transitions in TiO2 were studied by in situ X‐ray diffraction under high pressure up to 25 GPa and high temperature up to 900 °C. The phase of TiO2 was identified along various routes on the P‐T diagram; (i) rutile transforms directly to the baddeleyite phase at 12 GPa in the increasing pressure process and transforms back to the intermediate α‐PbO2 phase at around the same pressure in the decreasing pressure process at room temperature, and (ii) the baddeleyite ↔ α‐PbO2 reversible transition is confirmed with the temperature change at 16 GPa. These results give that the boundary between the α‐PbO2 and baddeleyite phases is expressed by the equation, T(°C)=188.7 P(GPa)‐2192.5. The phase transitions among the rutile, α‐PbO2 and baddeleyite phases at room temperature are explained well by the displacive mechanism.