Oxide-ion conductors are important as electrolytes in electrochemical devices such as Solid Oxide Fuel Cells (SOFCs) (to convert chemical fuels into electrical power). To reduce the operating temperature (currently ~ 800 oC) requires the discovery of new and improved oxide-ion conducting materials with high levels of conductivity between 200-600 oC. Recently we discovered a new family of oxide-ion conductors based on the perovskite (Na,Bi)TiO3 (NBT) with exceptional conductivity below 600 oC (Nature Materials, 13 (2014) 31-35). We propose to undertake a systematic study of the structure-composition-properties of other Bi-based perovskites and structurally related Aurivillius phases to elucidate the high oxide-ion conduction mechanism(s) and to improve further oxide-ion conducting electrolytes for low/intermediate temperature electrochemical applications. New materials will be used to construct prototype fuel cells, using architecture and methods recently established within the Functional Materials and Devices group.