NEUTRON POWDER INVESTIGATION OF TETRAGONAL AND CUBIC STABILIZED ZIRCONIA, TZP AND CSZ, AT TEMPERATURES UP TO 1400-K

A comparative study of tetragonal (Y-TZP, 3 mol% Y2O3) and cubic (CSZ, 15 mol% CaO) zirconia Powder samples was carried out to learn about a Possible structural origin of the superior ionic conductivity of TZP at low temperatures. Structure refinements including anharmonic temperature factors and oxygen occupancies as well as a qualitative analysis of the diffuse background revealed large differences especially of the anisotropy of thermal motion and the underlying disorder in both sam les. Diffusion pathways are restricted to layers in TZP, in contrast with a three-dimensional behaviour in CSZ. The structural arrangement of the tetragonal phase is slightly more favourable for conduction processes. More importantly, the higher concentration of oxygen vacancies in CSZ is less operative due to an immobilization of these charge carriers by coherent and incoherent microclustering at low temperatures, whereas the smaller number of vacancies in TZP is fully available for transport processes. At higher temperatures - as CSZ approaches the true thermodynamic stability field of the cubic structure - the stabilizing function of the microclusters decreases, the clusters dissolve and the ionic conductivity in CSZ becomes superior to that in TZP. No such processes take place in TZP. The behaviour in powdered samples differs from that in single crystals.