Conductivity and redox stability of double perovskite oxide SrCaFe_1+xMo_1-xO_6-δ (x = 0.2, 0.4, 0.6)

A series of new double perovskite oxides SrCaFe_1+xMo_1-xO_6-δ (x = 0.2, 0.4, 0.6) were synthesised by solid state reaction method. Synthesis of SrCaFe_1+xMo_1-xO_6-δ (x = 0.2, 0.4, 0.6) were achieved above 700 °C in 5% H₂/Ar, albeit with the formation of impurity phases. Introduction of calcium to Sr₂Fe_1+xMo_1-xO_6-δ (x = 0.2, 0.4, 0.6) was not successful in simultaneously improving the conductivity of these compounds, with a significant reduction in the formability observed with increasing calcium content. Phase stability upon redox cycling was not observed for SrCaFe_1+xMo_1-xO_6-δ (x = 0.2, 0.4, 0.6). Redox cycling of SrCaFe_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, with re-reduction at lower temperatures attaining between 0.1% and 58.4% of the initial conductivity observed after high temperature reduction. The conductivity of SrCaFe_1.2Mo_0.8O_6-δ in 5%H₂/Ar between 300 °C and 500 °C was around 73.5 Scm^-1. The reliance of these compounds on high temperature reduction is expected to limit their utility as SOFC anode materials, as the vulnerability to oxidation can have disastrous consequence for fuel cell durability.