Electrical properties of grain boundaries and size effects in samarium-doped ceria

Ce0.85Sm0.15O1.925 samples have been prepared using the glycine-nitrate process. The effects of microstructure on their electrical properties were investigated by X-ray diffraction, density measurements, scanning electron microscopy and AC impedance spectroscopy. The grain-boundary conductivities and total conductivities increase with decreasing grain size for sintered densities of 95% or greater. The bulk conductivities are nearly independent of grain size for sintered densities of 95% or greater. It is found that the space-charge potential is nearly independent of grain size and the increase of the conduction path width is responsible for the increase of the apparent specific grain-boundary conductivity. The power densities and current densities of single cells based on Ce0.85Sm0.15O1.925 electrolytes with different grain size are evaluated.