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

Fluorite oxides Ce_0.8Sm_0.1Ln_0.1O_1.9 (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 Ce_0.8Sm_0.1La_0.1O_1.9 had the highest electrical conductivity, σ_700 °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.