Conductivity and redox stability of new double perovskite oxide Sr_1.6K_0.4Fe_1+xMo_1−xO_6−δ (x = 0.2, 0.4, 0.6)

A series of new perovskite oxides Sr_1.6K_0.4Fe_1+xMo_1−xO_6−δ (x = 0.2, 0.4, 0.6) were synthesised by solid state reaction method. Synthesis of Sr_1.6K_0.4Fe_1+xMo_1−xO_6−δ (x = 0.2, 0.4, 0.6) was achieved above 700 °C in 5 % H₂/Ar, albeit with the formation of impurity phases. Phase stability upon redox cycling was only observed for sample Sr_1.6K_0.4Fe_1.4Mo_0.6O_6−δ. Redox cycling of Sr_1.6K_0.4Fe_1+xMo_1−xO_6−δ (x = 0.2, 0.4, 0.6) demonstrates a strong dependence on high temperature reduction to achieve high conductivities. After the initial reduction at 1200 °C in 5 %H₂/Ar, then re-oxidation in air at 700 °C and further reduction at 700 °C in 5 %H₂/Ar, the attained conductivities were between 0.1 and 58.4 % of the initial conductivity after reduction 1200 °C in 5 %H₂/Ar depending on the composition. In the investigated new oxides, sample Sr_1.6K_0.4Fe_1.4Mo_0.6O_6−δ is most redox stable also retains reasonably high electrical conductivity, ~70 S/cm after reduction at 1200 °C and 2–3 S/cm after redox cycling at 700 °C, indicating it is a potential anode for SOFCs.