Conductivity and redox stability of new double perovskite oxide Sr 1.6 K 0.4 Fe 1+ x Mo 1− x O 6− δ (x= 0.2, 0.4, 0.6)

A series of new perovskite oxides Sr1.6K0.4Fe1+xMo1−xO6−δ (x = 0.2, 0.4, 0.6) were synthesised by solid state reaction method. Synthesis of Sr1.6K0.4Fe1+xMo1−xO6−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 Sr1.6K0.4Fe1.4Mo0.6O6−δ. Redox cycling of Sr1.6K0.4Fe1+xMo1−xO6−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 Sr1.6K0.4Fe1.4Mo0.6O6−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

Effects of cobalt addition on structural, thermal and electrical properties of praseodymium-yttrium co-doped barium cerates

Effects of cobalt addition on structural, thermal and electrical properties of praseodymium-yttrium co-doped barium cerates have been investigated. Relative densities >98 % have been achieved after sintering at 1400 °C or 1500 °C for only 1 h. All studied compounds are stable in ambient air up to the measured 900 °C and, in reducing atmosphere (both wet and dry 5 % H2-Ar) up to the measured 800 °C. The Co-free sample (BaCe0.7Y0.2Pr0.1O3-δ) exhibits the highest conductivity of 1.21 × 10-2 S cm-1 at 700 °C in air while the corresponding cobalt containing sample (BaCe0.7Y0.175Pr0.1Co0.025O3-δ) has a conductivity of 9.85 × 10-3 S cm-1 at 700 °C in air. Cobalt addition allows the ability to retain much larger amounts of water to be retained as suggested by the higher conductivities obtained in wet hydrogen compared to the values in dry reducing atmosphere. This latter phenomenon is of special interest as it suggests the possibility of higher ionic conductivities in water-containing atmosphere and would benefit to intermediate- and high-temperature solid oxide fuel cells and/or electrolysers. The thermal expansion coefficients for the Co-free and Co-containing samples were around 12.0 × 10-6 K-1 between 25 and 1000 °C