Effects of alumina additions on sintering behavior of gadolinia-doped ceria

The effects of alumina additions on the sintering behavior of gadolinia-doped ceria were systematically investigated in terms of the variations in sintered density and grain size and the existing forms of Al2O3 in CeO2. Sintered density increased with increasing Al2O3 content up to 2 mol% and then it decreased with further addition of Al2O3. Grain size also increased with increasing Al2O3 content up to 2 mol% and then decreased with further addition of Al2O3. Decrease in grain size was caused by a pinning effect of Al2O3 precipitated at grain boundaries. Lattice constant decreased with increasing Al2O3 content up to 2 mol%. This decrease is due to the substitution of smaller Al3+ ions for Ce4+ ions in the CeO2 structure. According to the results obtained from SEM and XRD analyses, the solubility limit of Al2O3 in Ce0.8Gd0.2O1.9 ceramics was found to be nearly 2 mol%. The addition of Al2O3 up to the solubility limit was found to promote the sintering properties of Gd2O3-doped CeO2.