Structure and transport properties of vanadium substituted cerium niobate

Abstract

The effects of vanadium substitution on the structure and transport properties of CeNbO 4 + δ were investigated. Initial studies were via room temperature X-ray powder diffraction of the CeNb 1 − x V x O 4 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 CeNb 0.6V 0.4O 4 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 CeNb 1 − x V x O 4 series probed by AC impedance spectroscopy, highlighting an increase in conductivity with increasing vanadium substitution.