Revisiting the lattice dynamics of cubic yttria-stabilized zirconia

Cubic yttria-stabilized zirconia has long been a ceramic material of interest for its many uses in thermal-based applications. Its very low and weakly temperature-dependent thermal conductivity has been ascribed to the large oxygen vacancies content, which introduces disorder and strongly scatters phonons. Still, despite many experimental works in the literature, phonon dynamics has not been fully understood yet, with several points to be clarified, such as the apparent absence of optic modes throughout the Brillouin zone. In this paper, we present findings on the phonon dispersions of this material, showing experimental evidence of low-lying optical branches throughout the Brillouin zone, which reduce the pure acoustic regime for some branches. Furthermore, the observed energy dependence of the intrinsic acoustic phonon linewidths clearly suggests the existence of competing Mie and Rayleigh scattering mechanisms. Our findings allow to uncover a different phonon dynamics scenario in this material and point to a deeper understanding of heat transport in yttria-stabilized zirconia, based on two different, concomitant mechanisms, generated by the large vacancy content.