Abstract
The final phases of zirconia powders depend on the synthesis method employed, and the amounts of stabilizer present. In this study, ceria- and yttria-doped zirconia powders were prepared by urea hydrolysis and subsequent hydrothermal treatment. The amount of tetragonal (t) vs monoclinic (m) phase in the powders increased with increasing stabilizer content, while the tetragonal phase size decreased and the microstrain of t crystals remained unchanged. The thermal degradation behavior of the metastable t phase in zirconia containing a low CeO 2 or YO 1.5 doping level was explored during aging treatment by means of X-ray line profile broadening analysis. Both ultrafine yttria- and ceria-doped zirconia powder pellets exhibit isothermal t → m transformation after aging at 900°C for various times. It is argued that a crystallite size effect, rather than the dopant valence, dictates the occurrence of the t → m transformation in ultrafine zirconia powders. The change in crystallite sizes of both t and m phases during aging depends significantly on the amount of stabilizer, aging time, and mechanism of t → m phase transformation. However, the change of microstrain in both t and m phases is related to the amount of stabilizers present and the matrix constraints.