Citric-Nitrate Combustion Synthesis and Electrical Conductivity of the Sm3+ and Nd3+ Co-Doped Ceria Electrolyte

Nanocrystalline fluorite Ce0.8SmxNd0.2-xO1.9 (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 Ce0.8SmxNd0.2-xO1.9 pellets were successfully prepared by sintering these fine powders at 1400 degrees, 1500 degrees, and 1600 degrees C, respectively. The scanning electron microscopy pictures showed that the grain size of the pellet sintered at 1400 degrees C was between 500 nm and 2 mu m, while for the samples sintered at 1600 degrees C, the grains were coarser (6 mu m). The electrical conductivity of the sample sintered at 1400 degrees C was as high as 0.012 S/cm at 500 degrees 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.