Effects of fine alumina dispersion on ionic conductivity and mechanical properties of ytterbia stabilized cubic zirconia

Nanocomposites of Yb₂O₃ stabilized ZrO₂ (YbSZ) containing fine Al₂O₃ dispersions were fabricated by conventional powder mixing and a pressureless sintering technique. A fine homogeneous microstructure was obtained for the composites. This microstructural refinement decreased the size of defects in the composites, which significantly increased the fracture strength of the composites compared to that of monolithic ZrO₂. The composites had the same ionic conductivity values as those of the monolithic ceramics at high temperatures (in the range of 800 - 1000°C). Furthermore, the activation energy at high temperatures was independent of the Al₂O₃ content, whereas in the lower temperature regime (300 - 800°C), it varied with the Al₂O ₃ fraction. This indicated that different O^2- conduction-based activation processes were operating in the two temperature regimes. The O^2- ion transfer could easily occur at high temperatures due to the presence of the Al₂O₃ particulate dispersion in the composite system. From these results, it was concluded that the dispersion of fine grained Al₂O₃ into YbSZ is advantageous for achieving high-strength ion-conductive cubic zirconia.