A NEW COPPER-OXIDE SUPERCONDUCTOR CONTAINING CARBON

SUPERCONDUCTIVITY in the high-transition-temperature (high-T(c)) copper oxide superconductors seems to arise from layers of copper-oxygen squares, pyramids or octahedra. Recently the compound Sr2CuO2CO3 was found to contain layers of CuO6 octahedra 1 (Fig. 1), suggesting that it might be made superconducting by appropriate doping. But the presence of carbonate as an impurity is known to degrade the superconducting properties of materials such as YBa2Cu3O7-delta' and YBa2Cu4O8 (refs 2,3), much effort having been made to minimize residual carbon in these compounds by optimizing processing methods 4. It is thus of some interest to see whether Sr2CuO2CO3 can be made superconducting despite the carbonate ions incorporated in the structure. Here we report the synthesis, at 50 atm oxygen partial pressure, of superconducting (BaxSr1-x)2Cu1+yO2+2y+delta(CO3)1-y (0.4 less-than-or-equal-to x less-than-or-equal-to 0.65, y almost-equal-to 0.1), with T(c) (onset) up to approximately 40 K and zero resistance at up to approximately 26K. The crystal structure contains CuO2 sheets alternating with (BaxSr1-x)2CuyO2y+delta(CO3)1-y slabs, which serve as charge reservoir layers: substitution of approximately 10% copper for carbon in the slabs introduces holes into the CuO2 sheets, making the compound superconducting.