Processing and characterization of Sr2−xVMoO6−δ double perovskites

► Primary Sr2−xVMoO6−δ phase only shown to form in excess of 1300 °C in reducing. ► Surface formation of secondary phase SrMoO4−δ (Mo6+) observed at RT in air. ► Surface vanadium deficiency induced by inward atomic diffusion. ► Semiconductor to metallic transition is related to the reduction of Mo6+ to Mo4+