Synthesis and electrical characterisation of the tetragonal tungsten bronze type phases, (Ba/Sr/Ca/La)0 6MxNb1−xO3−δ (M=Mg, Ni, Mn, Cr, Fe, In, Sn): evaluation as potential anode materials for solid oxide fuel cells

We have synthesised a range of niobium-based tetragonal tungsten bronze materials of the form (Ba, Sr, Ca, La)0.6MxNb1−xO3 (M=Ni, Mg, Mn, Fe, Cr, In, Sn) to include both known phases and new materials. Electrical conductivity measurements over a wide range of oxygen partial pressures (p(O2)=10−20–1 atm.) have been performed at a temperature of 930°C in order to evaluate their potential as anode materials in Solid Oxide Fuel Cells. The compounds with M=Cr, Mn, Fe, Ni, Sn appear not to be suitable for such a role, either because of poor oxygen exchange kinetics, possibly due to low oxide ion conductivity or because of partial decomposition on prolonged heat treatment (4 days) at 1000°C in H2–Ar (5%:95%) atmospheres. On the other hand, the compounds with M=Mg, In showed quite good conductivity characteristics and were stable under the prolonged reduction treatment. The observed conductivities were, however, slightly lower than those observed previously for the related system (Ba, Sr, Ca)0.6Ti0.2Nb0.8O3, and were found to decrease with increasing M content, x.