Processing and characterization of Sr2−xVMoO6−δ double perovskites

In this study, the analysis and characterization of the processing and sintering of Sr2−xVMoO6−δ perovskites, where x = 0.0, 0.1 and 0.2, was investigated with application potential in high temperature fuel cell electrodes and electro-catalysts. Sr2−xVMoO6−δ substrates were sintered in a reducing (5%H2 95%N2) atmosphere at 1100 °C, 1200 °C, and 1300 °C. The X-ray diffraction patterns indicate that the double perovskite is the primary phase for Sr2−xVMoO6−δ pellets sintered at 1200 °C and 1300 °C for 20 h; however, these pellets show a secondary phase of SrMoO4−δ. X-ray photoelectron spectroscopy revealed a deficiency of vanadium on the pellet surfaces, in which samples yielded surface vanadium concentrations of less than 5%. The vanadium inhomogeneity can be explained by the formation of the SrMoO4−δ scheelite phase (ABO4) due to oxygen exposure on the surface of the pellets, which indicates inward vanadium migration to the bulk, and was exhibited in redox cycling. Sr2−xVMoO6−δ pellets sintered at 1300 °C showed the lowest resistivity at both SOFC operating temperature (800 °C) and room temperature. The resistivity tests also show a semiconductor to metallic transition for all double perovskites, from heating up to 800 °C to cooling down to room temperature in a reducing atmosphere, related to the reduction of Mo6+ to Mo4+.