Polycrystalline samples and thin films of the x = 0.8 member of the CexGd1-xO2-y solid solution have been successfully prepared. Their structural and transport properties have been studied by means of X-ray diffraction and electrical conductivity measurements as a function of preparation route, grain size, substrate nature and film thickness. Our data shows that the substrate roughness plays a relevant role in affecting the final a; however, by optimizing the thin films preparation conditions we showed that the conductivity of CGO material is always greater than that of the state-of-the-art oxide conductor, the YSZ 8 mol%, even though an electronic contribution ranging from 10% to 20% was found. (c) 2005 Elsevier B.V. All rights reserved.