A neutron scattering investigation of cubic stabilised zirconia (CSZ) .2. Lattice dynamics of Y- and Ca-CSZ

We have measured the acoustic phonon dispersion curves of three Cubic Stabilised Zirconias (CDZ) (9.5 and 24 mol% Y2O3- and 12.5 mol% CaO-ZrO2) at room temperature using a triple axis spectrometer. Phonons become broader and decrease in intensity as the Brillouin zone boundary is approached. The behaviour of the [zeta zeta 0]TA(1) branch is anomalous in that it broadens to the extent that it cannot be observed beyond 2 pi/a(0.4, 0.4, 0). To a lesser extent the same behaviour is observed for the other LA and TA branches. Despite an intensive search, we have not been able to measure any optic phonons. Previous workers have attributed these effects to the static disorder of the oxygen sublattice. In this paper, we present lattice dynamical calculations which model the effect of oxygen vacancies and relaxations which qualitatively explain the experimental phonon observations.