in this work, a variant of the sol-gel technique known as cation complexation was used for the preparation of Gadolinum-doped ceria (GDC) solid solution. This method has the advantage of low cost and relative simplicity. A range of techniques including X-ray diffraction (XRD), specific surface area determination (BET) and scanning electron microscopy (SEM) were employed to characterize the GDC powder. GDC calcined at 500 degrees C was found to have an average crystallite size of 10 nm. To obtain an insight into any changes in the electrolyte material during operation, the electrochemical properties of dense GDC samples were studied by impedance spectroscopy (IS) before and after simple ageing treatment in dry air at 800 degrees C for 40h. A reduction in grain boundary conductivity was observed after thermal treatment in the sample with the lower density. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.