Pressure‐Induced Phase Transformation of HfO ₂

The pressure dependence of the Raman spectra of HfO 2 was measured by a micro‐Raman technique using a singlecrystal 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 ZrO 2 . The space group for the high‐pressure phase of HfO 2 was determined as Pbcm , which was the same as that of the high‐pressure phase for ZrO 2 on the basis of the number and the spectral structure of the Raman bands.