A neutron scattering investigation of cubic stabilised zirconia (CSZ) .1. The average structure of Y-CSZ

Single crystal neutron diffraction has been used to study the relaxations of the O-atom from its ideal fluorite position in yttria stabilised cubic zirconia (Y-CSZ). The samples used in this study cover a compositional range of 9.5-24 mol% Y2O3 -ZrO2. We find that the O-atom is predominantly displaced in the [100] direction and to a lesser extent in the [111], while appreciable amounts remain at the ideal fluorite site. Further the average Zr-O distances decrease with Y2O3 content to values similar to that of tetragonal zirconia for compositions close to the cubic-tetragonal zirconia phase boundary. The controversy in the literature over the direction of relaxation of the O-atom is resolved with the aid of probability density functions. We demonstrate that there is more than one way to describe the distribution of the O-atom about its ideal site. A probability maximum is always produced at the ideal site, while probability density in the [100] directions is strong.