COPPER-OXIDE SUPERCONDUCTORS CONTAINING SULFATE AND PHOSPHATE GROUPS

Following observations that carbonate anions can be substituted into perovskite structutes containing Cu to yield superconducting phases, the possibility that other oxy-anions may behave similarly has been explored. Here we report the incorporation of sulphate and phosphate groups into the YBa2Cu3O7-delta structure, to form materials such as YSr2Cu2.79(SO4)0.21O6.16. The partial replacement of Y3+ ions by Sr2+ or Ca2+ ions injects holes into the CuO2 layers and results in a change from antiferromagnetic to superconducting behaviour with T(c)(onset) up to almost-equal-to 60 K. These mater-ials contain not only new charge reservoir layers but also novel superconducting CuO2 sheets with both 4-coordinate Cu (as in Nd2CuO4) and 5-coordinate Cu (as in YBa2Cu3O7).