Raman spectrometry study of phonon anharmonicity of hafnia at elevated temperatures

Raman spectra of monoclinic hafnium oxide HfO2 were measured at temperatures up to 1100 K. Raman peak shifts and broadenings are reported. Phonon dynamics calculations were performed with the shell model to obtain the total and partial phonon density of states, and to identify the individual motions of Hf and O atoms in the Raman modes. Correlating these motions to the thermal peak shifts and broadenings, it was found that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The hafniumdominated modes were more quasiharmonic and showed less broadening with temperature. Comparatively, the oxygen-dominated modes were more influenced by the cubic term in the interatomic potential than the hafnium-dominated modes. An approximately quadratic correlation was found between phonon-line broadening and softening.