Oxyanion derivatives of cuprate superconductors superconducting 123 phosphates

Abstract

While YSr₂Cu₃O₇ cannot be prepared under ambient conditions, partial substitution of the phosphate group for copper, as in YSr₂Cu_2.8(PO₄)_0.2O_y, stabilizes this phase in the orthorhombic structure, but the material is not superconducting. Superconductivity in YSr₂Cu_2.8(PO₄)_0.2O_y is obtained by increasing the hole concentration through partial substitution of Y by Ca, as in Y_0.7Ca_0.3Sr₂Cu_2.8(PO₄)_0.2O_y (T_c≈40 K). By incorporating the phosphate group in orthorhombic YBaSrCu₃O₇, a stable tetragonal derivative of the formula YSr₂Cu_2.8(PO₄)_0.2O_y (T_c≈47 K) has been prepared; the T_c increases to ~70 K by partial substitution of Y by Ca as in Y_0.7Ca_0.3BaSrCu_2.8(PO₄)_0.2O_y.