In this paper we report the synthesis and characterisation of the perovskite cuprate phases YSr 2 Cu 2 MO 7+y (M=Co, Fe) to examine their potential for use as cathode materials in Solid Oxide Fuel Cells (SOFC). Both samples showed conductivities of ≈10 Scm -1 at 900°C and were also shown to be stable at this temperature in N 2 . For YSr 2 Cu 2 FeO 7+x , semiconducting behaviour was observed up to ≈550°C, with a decrease in conductivity at higher temperatures, attributed to oxygen loss reducing the charge carrier concentration.In the case of YSr 2 Cu 2 CoO 7+y , semiconducting behaviour was observed over the range of temperatures studied, although a small but significant steep increase in conductivity was observed above 800°C. High temperature X-ray diffraction studies of this particular phase showed that this increase in conductivity coincided with an orthorhombictetragonal structural transition, accompanied by a significant reduction in cell volume. In addition to measurements in air, conductivities were also measured with varying p(O 2 ) (0.2-10 -5 atm.) at 900°C, and this data showed significant hysteresis between measurements on reducing and re-oxidising, suggesting poor oxide ion transport, poor oxygen surface exchange kinetics, or significant structural changes on varying p(O 2 ).Chemical compatibility studies of these phases with SOFC electrolytes at temperatures between 900 and 1000°C showed reaction in all cases. In the case of CeO 2 based electrolytes, the reaction led to the formation of the "fluorite-block" phases, (Y/Ce) 2 Sr 2 Cu 3-x M x O 9+y (M=Co, Fe), and samples of these were subsequently prepared and the conductivities measured. Similar hysteresis between conductivity measurements on reducing and re-oxidising were also observed for these samples.

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