Thermally activated rotation of Co1−xO particles within zirconia grains

Yttria partially stabilized zirconia (Y-PSZ) and Co1−xO powders in 4:1 molar ratio were sintered and then annealed at 1300 and 1600°C to investigate the orientation change of Co1−xO particles within Y-PSZ grains. Transmission electron microscopic observations indicated the Co1−xO particles remained nonepitaxy in Y-PSZ grains after annealing at 1300°C for 300 h. When fired at 1600°C for 1–100 h, submicro-sized Co1−xO particles (denoted as C) reached parallel epitaxy relationship, i.e. [100]C//[100]Z, [010]C//[010]Z and another relationship, i.e. [111]C//[100]Z, [11̇0]C//[011]Z with respect to the host zirconia grain (denoted as Z) nearly free of tetragonal precipitates. On the other hand, larger intragranular Co1−xO particles (>1 μm in diameter) failed to reach epitaxial orientations even subject to prolonged annealing (100 h) at 1600°C. The temperature and size dependence of orientation change of the intragranular particle is in accordance with theoretical consideration of Brownian type rotation of the particle above a critical temperature for anchorage release at interface.