The effects of vanadium substitution on the structure and transport properties of CeNbO4+delta were investigated. Initial studies were via room temperature X-ray powder diffraction of the CeNb1-xVxO4 series (x=0, 0.2, 0.4, 0.6, 0.8 and 1) identifying three distinct phases; monoclinic fergusonite (I2/a), tetragonal wakefieldite (I4(1)/amd and tetragonal scheelite (I4(1)/a). The scheelite phase occurred at a stoichiometry of CeNb0.6V0.4O4 and is of interest due to its open fluorite-like structure believed to be beneficial for oxide ion conduction. This phase was therefore the main focus of the investigation and was examined using high temperature X-ray diffraction, thermogravimetric analysis and dilatometry, all of which identified a thermally and redox stable phase in contrast to the parent material. The room temperature structure was confirmed using neutron powder diffraction and the transport characteristics of the CeNb1-xVxO4 series probed by AC impedance spectroscopy, highlighting an increase in conductivity with increasing vanadium substitution. (c) 2008 Elsevier B.V. All rights reserved.