Bulk superconductivity at 91 K in single-phase oxygen-deficient perovskite Ba2YCu3O9-<>

We have prepared and identified as a single phase the high-temperature superconducting compound in the chemical system Y-Ba-Cu-O, an orthorhombic, distorted oxygen-deficient perovskite of stoichiometry Ba2YCu3O9-<> (<>2.1). Samples exhibit zero resistance at 91 K, with a transition width of 1.5 K. The Meissner effect attains a value of 76% of the independently measured diamagnetic susceptibility. We estimate parameters that characterize this superconductor, e.g., <>3<>5 mJ (mole Cu)-1 K-2. The critical current density at 77 K and H=0 exceeds 1100 A/cm2.