Effect of morphology and space charge on conduction through porous doped ceria

Porous samples of samaria (Sm2O3)-doped ceria (CeO2) (SDC) were fabricated using two methods: (1) conventional sintering of powder compacts; and (2) fabrication of sintered NiO + SDC two-phase samples, reduction of NiO to Ni, and acid leaching of Ni. Electrical conductivities of as-fabricated bar samples were measured using a four-probe DC technique. The conductivity of samples made by acid leaching of Ni was up to two orders of magnitude higher than that of conventionally fabricated samples of the same porosity. This difference was attributed to differences in relative inter-particle neck sizes. A simple analytical model was developed to describe conductivity of porous bodies in terms of inter-particle neck sizes. The total electrical conductivity of samples fabricated by the leaching process was measured as a function of oxygen pressure and temperature. The effect of space charge was included in the model describing electrical conduction through porous bodies. The adverse effects of space charge on conductivity are more pronounced in porous ceria as compared to dense ceria.