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

The microstructure, thermal expansion, microhardness, indentation fracture toughness, and ionic conductivity of neodymium-doped ceria (NDC) prepared by coprecipitation were investigated. The results revealed that the average particle size (DBET) ranged from 20.1 to 25.8 nm, crystallite dimension (DXRD) varied from 17.5 to 20.7 nm, and the specific surface area distribution was from 31.25 to 40.27 m2/g for neodymium-doped ceria stacking powders. Dependence of lattice parameter, a, versus dopant concentration, x, of Nd3+ ion shows that these solid solutions obey Vegard's rule as a(x) = 5.4069 + 0.1642x for Ce1−xNdxO2−(1/2)x for x = 0.05–0.25. For neodymium-doped ceria ceramics sintered at 1500 °C for 5 h, the bulk density was over 95% of the theoretical density. The maximum ionic conductivity, σ800°C = 4.615 × 10−2 S/cm, with the minimum activation energy, Ea = 0.794 eV was found for the Ce0.75Nd0.25O1.875 ceramic. Trivalent, neodymium-doped ceria ceramics revealed high fracture toughness, the fracture toughness distribution was in the range of 6.236 ± 0.021 to 6.846 ± 0.017 MPa m1/2. The high indentation fracture toughness of neodymium-doped ceria was attributed to crack deflection. Moreover, the porosity may influence the mechanical properties such as microhardness and fracture toughness. It was observed that as the porosity reduced, the microhardness and fracture toughness increased.