Synthesis and electrical properties of co-doping with La3+, Nd3+, Y3+, and Eu3+ citric acid-nitrate prepared samarium-doped ceria ceramics

Fluorite oxides Ce0.8Sm0.1Ln0.1O1.9 (denoted as SDC for singular doping and LnSDC for Ln=La, Nd, Y and Eu), were prepared by the citric acid–nitrate combustion reaction to act as electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFC). The thermal decomposition, phase identification, morphology, density, particle size distribution and electrical properties of the samples were studied by TGA/TDA, XRD, SEM, the Archimedes method, a laser size analyzer and Impedance spectroscopy, respectively. All crystallite powders that calcined at 800 °C had a cubic fluorite structure; the average crystallite size was between 63 and 68.5 nm. The pellets were then sintered at 1400 °C in air for 7 h. The relative densities of these pellets were over 95%, which was in good agreement with the results of the SEM. The impedance measurements were performed in an open circuit using two electrode configurations. The results showed that Ce0.8Sm0.1La0.1O1.9 had the highest electrical conductivity, σ700 °C, equal to 6.59×10−2 S cm−1 and the lowest activation energy equal to 0.85 eV. It was therefore concluded that co-doping with the appropriate rare-earth cations can further improve the electrical properties of ceria electrolytes.