Preparation and characterization of samaria-doped ceria electrolyte materials for solid oxide fuel cells

The microstructure, thermal expansion, mechanical property, and ionic conductivity of samaria-doped ceria (SDC) prepared by coprecipitation were investigated in this paper. The results revealed that the average particle size ranged from 10.9 +/- 0.4 to 13.5 +/- 0.5 nm, crystallite dimension varied from 8.6 +/- 0.3 to 10.7 +/- 0.4 nm, and the specific surface area distribution ranged from 62.6 +/- 1.8 to 76.7 +/- 2.2 m(2)/g for SDC powders prepared by coprecipitation. The dependence of lattice parameter, a, versus dopant concentration, x, of Sm3+ ion shows that these solid solutions obey Vegard's rule as a (x)=5.4089+0.10743x for Ce1-xSmxO2-1/2x. For SDC ceramics sintered at 1500 degrees C for 5 h, the bulk density was over 95% of the theoretical density; the maximum ionic conductivity, sigma(800 degrees C)=(22.3 +/- 1.14) x 10(-3) S/cm with minimum activation energy, E-a=0.89 +/- 0.02 eV, was found in the Ce0.80Sm0.20O1.90 ceramic. A dense Ce0.8Sm0.2O1.9 ceramic with a grain size distribution of 0.5-4 mu m can be obtained by controlling the soaking time at 1500 degrees C. When the soaking time was increased, the microhardness of Ce0.8Sm0.2O1.9 ceramic increased, the toughness slightly decreased, which was related to grain growth with the soaking time.