X-ray diffraction study of hafnia under high pressure using synchrotron radiation

HfO2 was studied to 20 GPa at ambient temp. using synchrotron energy-dispersive x-ray powder diffraction methods. Traces of the initial monoclinic (baddeleyite) phase could still be identified at 20 GPa, but a phase transition begins at 2.6 GPa to HfO2 II, the lines of which can be indexed on an orthorhombic cell (Pbcm, Z = 4). The relative intensities of the (111) and (-111) monoclinic reflections suggests that a further phase change may begin near 10 GPa but work at high temps. is needed to establish this. The bulk compressibility of HfO2 is 1.2 × 10-4 kbar-1. A Rietveld anal. of the baddeleyite phase gave results in close agreement with earlier work but showed the sample to be internally strained. [on SciFinder(R)]