PRESSURE-INDUCED PHASE-TRANSFORMATION OF HFO2

The pressure dependence of the Raman spectra of HfO2 was measured by a micro-Raman technique using a single-crystal specimen in the pressure range from 0 to 10 GPa at room temperature. The symmetry assignment of Raman bands of the monoclinic phase was experimentally accomplished from the polarization measurements for the single crystal. With increased pressure, a phase transformation for the monoclinic phase took place at 4.3 +/- 0.3 GPa. Nineteen Raman bands were observed for the high-pressure phase. The spectral structure of the Raman bands for the high-pressure phase was similar with those reported previously for ZrO2. The space group for the high-pressure phase of HfO2 was determined as Pbcm, which was the same as that of the high-pressure phase for ZrO2 on the basis of the number and the spectral structure of the Raman bands.