The grain boundary effect in heavily doped cerium oxide

Microcrystalline cerium oxide ceramics, doped with Y, La or Gd in the concentration range between 0.1 and 27 at.% were prepared and their electrical conductivity was investigated. The bulk and total conductivities were determined by analyzing impedance spectra according to the brick-layer model. The grain boundary effect, which is indicated by the gap between the bulk and the total conductivity, was found to decrease rapidly as the acceptor concentration increases, in agreement with earlier results in literature. The experimental data were compared with results obtained from a model, in which the grain boundary effect is attributed to the presence of space charge layers. This comparison revealed that the evolution of the grain boundary effect is consistent with the intrinsic space charge model under the assumption of non-equilibrium distributions of acceptor ions.