A Raman Spectrometry Study of Phonon Anharmonicity of Zirconia at Elevated Temperatures

Raman spectra of monoclinic zirconia (ZrO_2) were measured at temperatures of up to 950 K. Temperature-dependent Raman peak shifts and broadenings were reported and compared with prior results on hafnia (HfO_2). Lattice dynamics calculations were performed with both shell model and density functional theory to obtain Raman frequencies, and the total and partial phonon density of states. These calculations were also used to identify the individual motions of metal and oxygen atoms in the different Raman modes. By correlating these motions to the thermal peak shifts and broadenings, it was confirmed that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The metal-dominated modes were found to be more quasiharmonic, and thus showed less broadening with temperature. Mass effects were evident by comparing the mode softening and shifting between zirconia and hafnia.