Citric-nitrate combustion synthesis and electrical conductivity of the Sm³⁺ and Nd³⁺ co-doped ceria electrolyte

Nanocrystalline fluorite Ce_0.8Sm_xNd _0.2-xO_1.9 (x=0.2, 0.15, 0.1, 0.05, and 0) powders were prepared by a citric-nitrate combustion process and the grain sizes were determined to be 10-20 nm from X-ray diffraction patterns. Dense Ce _0.8Sm_xNd_0.2-xO_1.9 pellets were successfully prepared by sintering these fine powders at 1400°, 1500°, and 1600°C, respectively. The scanning electron microscopy pictures showed that the grain size of the pellet sintered at 1400°C was between 500 nm and 2 μm, while for the samples sintered at 1600°C, the grains were coarser (6 μm). The electrical conductivity of the sample sintered at 1400°C was as high as 0.012 S/cm at 500°C and the activation energy was determined to be 0.63 eV. The mechanism of improved electrical conductivity in this codoping ceria solid solution is discussed.