DIFFUSION-INDUCED GRAIN-BOUNDARY MIGRATION IN CERIA-STABILIZED TETRAGONAL ZIRCONIA POLYCRYSTALS

The microstructure and microchemistry of grain-boundary regions in (CeO2 + La2O3)-stabilized tetragonal ZrO2 polycrystals (Ce(La)-TZP) were studied by means of transmission electron microscopy (TEM). Evidence was found for the existence of crystalline and vitreous intergranular phases situated in small pockets at multiple grain junctions and in thin films along grain boundaries. In this ceramic system grain-boundary migration was observed in situ in the TEM in sample areas subjected to electron irradiation. Interfaces migrated away from their centers of curvature. Evidence was found for Ce de-alloying in the volume swept by the advancing boundaries. It is suggested that the coherency lattice strain brought about by a partial reduction of Ce, resulting in the diffusion of Ce3+ along grain boundaries to free surfaces, is the driving force for this phenomenon.