Effect of grain size on the electrical properties of samaria-doped ceria solid electrolyte

Samaria-doped ceria (SDC) ceramic nanopowders have been synthesized by three different methods: co-precipitation, combustion, and hydrothermal. The Ce0.8Sm0.2O1.9 nanopowder with an average aggregate size of 47 nm and crystallite size of 7-11 nm prepared by the hydrothermal method has been used for further consolidation by pressureless (PLS) and spark plasma (SPS) consolidation methods at 1000-1400 degrees C to obtain dense ceramic samples with different grain sizes in the wide range of 80 to 1500 nm. The total electrical conductivities of 0.010-0.015 S/cm at 600 degrees C were obtained for the PLS-derived samples. The dense SDC nanostructured ceramics consolidated by SPS showed the very low activation energy of only 0.66 eV at temperatures of 300-400 degrees C, and the total electrical conductivity of 0.0056 S/cm. The enhancement of the grain-boundary framework quality by annealing of the nano-SDC electrolyte at 1000 degrees C for 20 hours almost doubled the average grain size. In addition the electrical conductivity was enhanced almost 40%, while keeping the activation energy unchanged.