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

The effects of gallia additions on the sintering behavior of gadolinia-doped ceria were systematically investigated from the following aspects: the variation in sintered density, the variation in grain size, and the existing forms of Ga 2O 3 in CeO 2. Sintered density increased with increasing Ga 2O 3 content up to 5 mol.% and then it decreased with further addition of Ga 2O 3. Grain size also increased with increasing Ga 2O 3 content up to 5 mol.% and then decreased with further addition of Ga 2O 3. Decrease in grain size was caused by a pinning effect of Ga 2O 3 precipitation at grain boundaries. Lattice constant decreased with increasing Ga 2O 3 content up to 5 mol.%. This decrease will be due to the substitution of smaller Ga 3+ ions for Ce 4+ ions in the CeO 2 structure. According to the results obtained from scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses, the solubility limit of Ga 2O 3 in Ce 0.8Gd 0.2O 1.9 ceramics can be estimated to be nearly 5 mol.%. The addition of Ga 2O 3 up to the solubility limit was found to promote the sintering properties of Gd 2O 3-doped CeO 2.