A NEUTRON-SCATTERING INVESTIGATION OF CUBIC STABILIZED ZIRCONIA (CSZ).2. LATTICE-DYNAMICS OF Y-CSZ 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-Zr O2) at room temperature using a triple axis spectrometer. Phonons beco me broader and decrease in intensity as the Brillouin zone boundary is approached. The behaviour of the [zeta zeta 0]TA(1) branch is anomalo us 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 observe d for the other LA and TA branches. Despite an intensive search, we ha ve not been able to measure any optic phonons. Previous workers have a ttributed these effects to the static disorder of the oxygen sublattic e. In this paper, we present lattice dynamical calculations which mode l the effect of oxygen vacancies and relaxations which qualitatively e xplain the experimental phonon observations.