Structural phase transitions in brookite-type TiO2 under high pressure

We have studied polycrystalline brookite TiO2 using energy-dispersive X-ray diffraction at pressures up to 27.8 GPa and derived an ambient-pressure bulk modulus of 255 GPa using Birch-Murnaghan's equations of state with a fixed value of 4 as its first derivative. The transition from brookite-type to baddeleyite-type was observed to start at 15.8 GPa and finished at 22.8 GPa. Upon decompression, the α-PbO2 structure appeared at 3.5 GPa and the baddeleyite-type structure remained down to 1.6 GPa, the lowest pressure in the present work.