THE STRUCTURE AND CRYSTALLISATION OF NANOCRYSTALLINE ZIRCONIA

M.G.Tucker and V.M.Nield

School of Physical Sciences, University of Kent, Canterbury, Kent, CT2 7NR

Neutron and X-ray diffraction, together with EXAFS, have been used to try and elucidate the structure of nanocrystalline zirconia, especially in its early stages of crystallisation from the hydroxide. In this paper results are presented of a detailed examination of the structural changes involved in the formation of nanocrystalline zirconia from zirconium hydroxide precursors. These precursors were prepared using both sol-gel and precipitation methods.

The preparation method and level of yttrium dopant in the sample both seem to affect the initial temperature of crystallisation, which can vary over tens of degrees about 350^oC. Detailed studies of the changes in Bragg peak width and intensity as a function of temperature and time in the very early stages of crystallisation are shown. These show that the rate of crystallisation is very different between sol-gel and precipitation method samples. The crystalline development at higher temperatures for samples prepared via the precipitation method has also been examined and found to be mainly temperature rather than time dependent. The crystallite growth may consist of two stages, with crystallites forming initially at the crystallisation temperature, then at 500^oC enough energy becomes available to overcome the grain boundaries and a second growth stage is evident. The neutron diffraction data shows unequivocally that hydroxyl groups remain in the samples even up to 700^oC. Hence a comprehensive picture of the growth process has been obtained.