GRAIN-BOUNDARY EFFECT ON CERIA BASED SOLID-SOLUTIONS

This work deals with the 'grain boundary effect' on electrical conduction in oxide solid solutions with fluorite structure. Ceria is chosen as basic oxide and doped with CaO. Impedance spectroscopy technique is used to determine the grain boundary contribution to the total polarization of the cell. Single, bi- and polycrystalline samples were investigated. Experiments were carried out between 250 and 700 degree C. Experimental results have shown the same behavior for the different cells as far as the bulk conductivity is concerned. Secondly, the grain boundary resistance decreases when the dopant content increases. Finally, the influence of grain boundary parallel to the electric field is negligible compared to that of the perpendicular one. Scanning electron microscopy (SEM) observations have shown an enhancement of calcium at grain boundaries. Taking into account this information, a simple model is proposed to report on grain boundary resistance in polycrystalline samples.