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 YSr2Cu2.8(PO4)0.2Oy, stabilizes this phase in the orthorhombic structure, but the material is not superconducting. Superconductivity in YSr2Cu2.8(PO4)0.2Oy is obtained by increasing the hole concentration through partial substitution of Y by Ca, as in Y0.7Ca0.3Sr2Cu2.8(PO4)0.2Oy (Tc≈40 K). By incorporating the phosphate group in orthorhombic YBaSrCu3O 7, a stable tetragonal derivative of the formula YBaSrCu2.8(PO4)0.2Oy (Tc≈ 47 K) has been prepared; the Tc increases to ∼ 70 K by partial substitution of Y by Ca as in Y0.7Ca0.3BaSrCu2.8(PO4)0.2Oy.