Powders of Gd-doped ceria solid solutions, Ce1−xGdxO2−δ (x = 0.05, 0.1, 0.2, 0.3 and 0.4), were prepared by using a freeze-drying precursor route. Dense ceramic pellets, with average grain sizes in the range of several μm, were obtained by sintering at 1600C. Cobalt nitrate was added to the powders in order to obtain dense ceramic samples having grain sizes in the sub-μm range at 1150C. The ionic conduction was analyzed by impedance spectroscopy in air, in order to deconvolute the bulk and grain boundary contributions. The bulk conductivity at low temperatures clearly decreased with increasing Gd content, whereas the activation energy increased. An alternative method was proposed for analyzing the extent of defect interaction upon conduction. For samples without added Co, the specific grain boundary conductivity increased with increasing Gd content. The addition of Co did not alter the bulk properties but produced a large increase in the specific grain boundary conductivity; mainly in samples with lower Gd-concentrations (x = 0.05 or 0.1). The segregation of Gd, and its strong interaction with charge carriers, could explain the blocking effects of grain boundaries.

Re-Examination of Bulk and Grain Boundary Conductivities of Ce1−xGdxO2−δ Ceramics. D.Pérez-Coll, P.Núñez, J.C.Ruiz-Morales, J.Peña-Martínez, J.R.Frade: Electrochimica Acta, 2007, 52[5], 2001-8