Electrical properties of ceria Co-doped with Sm 3+ and Nd 3+

Ceria co-doped with Sm ³⁺ and Nd ³⁺ powders are successfully synthesized by citric acid-nitrate low-temperature combustion process. In order to optimize the electrical properties of the series of ceria co-doped with Sm ³⁺ and Nd ³⁺, the effects of co-doping, doping content and sintering conditions on grain and grain boundary conductivity are investigated in detail. For the series of Ce _0.9(Sm _xNd _{1- x}) _0.1O _1.95 (x = 0, 0.5, 1) and Ce _{1- x}(Sm _0.5Nd _0.5) _xO _δ (x = 0.05, 0.10, 0.15, 0.20) sintered under the same condition, Ce _0.9(Sm _0.5Nd _0.5) _0.1O _1.95 exhibits both higher grain and grain boundary conductivity. Compared with Ce _0.9Gd _0.1O _1.95 and Ce _0.8Sm _0.2O _1.9, Ce _0.9(Sm _0.5Nd _0.5) _0.1O _1.95 sintered at 1350-1400 °C shows higher total conductivity with the value of 1.0 × 10 ^-2 S cm ^-1 at 550 °C. In addition, it can be found the trends of grain and grain boundary activation energies of Ce _{1- x}(Sm _0.5Nd _0.5) _xO _δ are both consistent with those of Ce _{1- x}Nd _xO _δ, but different from those of Ce _{1- x}Sm _xO _δ, which can be explained as: the local ordering of oxygen vacancies maybe occurs more easily in Nd-doped ceria than in Sm-doped ceria; the segregation amount of Sm ³⁺ is more than that of Nd ³⁺ to the grain boundaries in ceria co-doped with Sm ³⁺ and Nd ³⁺, which is confirmed by X-ray photoelectron spectroscopy (XPS).