X-RAY-DIFFRACTION STUDY OF TIO2 UP TO 49 GPA

TiO2 (anatase) was studied up to 49 GPa in a diamond anvil cell by angle-dispersive X-ray diffraction. Two phase transitions were observed, the first to the orthorhombic alpha-PbO2-type phase and the second to a monoclinic phase, which appears to be baddeleyite-stuctured. Birch-Murnaghan equations of state were calculated for both anatase and the alpha-PbO2-type phase yielding B0 values of 59(5) and 98(9) GPa, respectively. Accordingly, anatase is four times and the alpha-PbO2 phase twice as compressible as rutile. The high-pressure, monoclinic phase, in contrast, was found to be much harder than rutile.