The solid solubility limit of Al2O3 and its effect on densification and microstructural evolution in cubic-zirconia used as an electrolyte for solid oxide fuel cell

The solid solubility of Al2O3 in 8 mol% yttria-stabilized cubic zirconia (8YSCZ) was determined by XRD as a function of composition based on the lattice parameter change. It was seen that the average lattice parameter of 8YSCZ linearly decreased from 5.139 to 5.134 Å, as the Al2O3 content increased up to 0.3 wt% and the parameter did not vary with further increase in the Al2O3 content. This linearity shows that solid solubility limit of Al2O3 in 8YSCZ is about 0.3 wt%. The lower values of the lattice parameter found for Al2O3-doped 8YSCZ could be due to the dissolution in the cubic phase of some Al2O3 which has a smaller ionic radius than Zr+4 and Y+3 and thus replacing the smaller Al+3 ions with Zr+4 and Y+3 in the cubic lattice. It was also seen that the amount of solid solution affected densification and grain growth behaviour of 8YSCZ. Particularly, Al2O3 addition up to solubility limit of 0.3 wt% enhanced the densification and grain growth whereas further increase in Al2O3 content over solubility limit resulted in decreased densification and grain growth.