Pressure-induced phase transformation of HfO2

This paper reports on the pressure dependence of the Raman spectra of HfO2 that 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