Effect of Tb co-dopant on the electrical conductivity of Sm-doped ceria electrolyte

Series of solid solutions of (Ce0.85Sm0.15)1 − xTbxO2 − δ with x = 0–0.05 were synthesized by glycine–nitrate process. All prepared (Ce0.85Sm0.15)1 − xTbxO2 − δ (x = 0–0.05) powders were sintered at 1250 °C, 1350 °C and 1450 °C, respectively. X-ray diffraction patterns indicate that all samples crystallize to a single phase of cubic fluorite structure. Higher sintering temperature was found to give lower electrical conductivity and higher activation energy for (Ce0.85Sm0.15)1 − xTbxO2 − δ (x = 0–0.05). The lower sintering temperatures suppress grain growth giving rise to small grain size. The samples sintered at lower temperatures showed higher grain boundary conductivities, which results in the increasing of total electrical conductivity. The change of electrical conductivities of solid solutions for (Ce0.85Sm0.15)1 − xTbxO2 − δ (x = 0–0.05) was not obvious, and the maximum conductivity was found at x = 0.01 when sintered at1250 °C. The reason may be that co-doping 0.01 terbium in doped ceria will increase the oxygen vacancy concentration slightly, increasing dopant concentration, the oxygen vacancy Vo and the dopants Tb′Ce and Sm′Ce tend to associate and form [Vo Tb′Ce] and [Vo Sm′Ce] pairs, resulting in a decrease in [Vo].