The solid solubility limit of Al 2O 3 and its effect on densification and microstructural evolution in cubic-zirconia used as an electrolyte for solid oxide fuel cell

Abstract

The solid solubility of Al 2O 3 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 Al 2O 3 content increased up to 0.3 wt% and the parameter did not vary with further increase in the Al 2O 3 content. This linearity shows that solid solubility limit of Al 2O 3 in 8YSCZ is about 0.3 wt%. The lower values of the lattice parameter found for Al 2O 3-doped 8YSCZ could be due to the dissolution in the cubic phase of some Al 2O 3 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, Al 2O 3 addition up to solubility limit of 0.3 wt% enhanced the densification and grain growth whereas further increase in Al 2O 3 content over solubility limit resulted in decreased densification and grain growth.