Preparation and property–performance relationships in samarium-doped ceria nanopowders for solid oxide fuel cell electrolytes

Abstract

In a systematic study, Samarium doped ceria (SDC) nanopowders, SmxCe1−xO2−x/2 (x=0.1, 0.2 or 0.3), were prepared by a low temperature citrate complexation route. The synthesis and crystallisation of the SDC powders were followed by thermochemical techniques (TGA/DTA), X-ray diffraction, elemental analysis, specific surface area determination (BET) and electron microscopy (SEM and TEM). Mean crystallite sizes were found to be around 10nm for all compositions calcined at 500°C. Dense electrolyte bodies were prepared at 1300°C, 1400°C and 1450°C using two sintering times, 4h or 6h. Densities of 91–97% of theoretical were obtained, with a marked improvement in density on going from 1300°C to higher sintering temperatures. Grain size analysis was conducted using SEM. Grain size distributions were related to %Sm and sintering conditions. Impedance spectroscopy was used to determine the total, bulk and grain boundary conductivities, the related activation energies and enthalpies of defect association and ion migration. Sintering at 1400°C/6h or 1450°C/4h gave superior grain structure and conductivity, with oversintering occurring after more severe treatments. At 600°C the highest total ionic conductivity was 1.81×10−2Scm−1 for Sm0.2Ce0.8O1.9. The relationships between chemical composition, sintering parameters, grain structure and electrochemical performance are discussed.