CeNbO4+d (0 <= d <= 0.33) displays mixed ionic-electronic conductivity at ~800 °C, where it adopts the tetragonal scheelite structure. Prior research has shown that partial substitution of Nb with V can lower the temperature of this transition, opening up the possibility of improved conductivity at temperatures closer to the “intermediate” range favoured for solid oxide fuel cell (SOFC) devices (500-700 °C). We will use quasielastic neutron scattering to study in detail the diffusion behaviour of oxide ions within the conductive scheelite phase of Ce(Nb,V)O4+d. Large single-crystal samples will enable to examine the distinct directional components of oxygen diffusion and compare the conduction behaviour to that determined theoretically for CeNbO4 and other candidate SOFC electrode materials with the scheelite structure.