Polarized Raman spectra of tetragonal pure ZrO 2 measured on epitaxial films

The actual ambiguity in the interpretation of the Raman-active vibrations of tetragonal ${\mathrm{ZrO}}_{2}$ is discussed as a factor impeding progress in long-standing investigations of the polymorphism of zirconia. The reliable symmetry assignment of these vibrations is proposed by analyzing a polarized light scattering from single-crystal grains of epitaxial films of pure $t\ensuremath{-}{\mathrm{ZrO}}_{2}$ grown on monocrystalline ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ samples. The interrelations between the Raman spectrum of $t\ensuremath{-}{\mathrm{ZrO}}_{2}$ and the relevant phonons of $c\ensuremath{-}{\mathrm{ZrO}}_{2}$ are considered, implying the ${A}_{1g}$ vibration as a soft mode driving the tetragonal-cubic transformation.