Effects of Additives on Sintering Behavior of Gadolinia-Doped Ceria

Abstract

The effects of sintering additives such as Al₂O₃ and Ga₂O₃ 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 and Ga₂O₃ in CeO₂. Both sintered density and grain size increased with increasing additive content up to 2 mol% for Al₂O₃ addition and up to 5 mol% for Ga₂O₃ addition. However, they decreased with further addition of the additives. At a higher additive content, grain size decreased by a pinning effect of the precipitates at grain boundaries. Lattice constant decreased with increasing additive content up to 2 mol% for Al₂O₃ addition and up to 5 mol% for Ga₂O₃ addition. This decrease will be due to the substitution of smaller Al³⁺ ions or Ga³⁺ ions for Ce⁴⁺ ions in the CeO₂ structure. The solubility limits of additives in Ce_0.8Gd_0.2O_1.9 ceramics estimated using the results obtained from SEM and XRD analyses were about 2 mol% for Al₂O₃ addition and 5 mol% for Ga₂O₃ addition. The addition of Al₂O₃ or Ga₂O₃ up to the solubility limit was found to promote the sintering properties of Gd₂O₃-doped CeO₂.