Additions of excess of Gd were used to demonstrate that designed heterogeneities may yield enhanced grain boundary conductivity of ceria-gadolinia ceramic samples sintered at temperatures from 1400 degrees C to 1500 degrees C. Additions of excess of Ce play negative effects. Microstructural contributions of the overall electrical behavior were de-convoluted by electrochemical impedance spectroscopy. Though the bulk conductivity is nearly independent of sintering temperature and almost insensitive to compositional heterogeneities, the specific grain boundary conductivity shows strong dependence on these two factors. Estimates of grain boundary thickness indicate that sintered samples retain compositional heterogeneities with significant effects on space charge potentials. (C) 2012 Elsevier Ltd. All rights reserved.