Bulk superconductivity at 91K in single phase oxygen deficient perovskite Ba sub 2 YCu sub 3 O sub (9-delta).

We have prepared and identified as a single phase the high temperature superconducting compound in the Y-Ba-Cu-O chemical system. The compound, is a distorted oxygen-deficient perovskite of stoichiometry Ba sub 2 YCu sub 3 O sub (9-delta) (delta sup ~ 2.1). Samples prepared in oxygen exhibit zero resistance at 91K, with a resistive transition width of 1.5K. The Meissner effect starts at the same temperature, attaining at lower temperatures a value of 76% of the independently measured diamagnetic susceptibility. Based on resistivity and critical field measurements, we estimate parameters that characterize this superconductor, e.g., x sup ~ 3.5 mJ/mole Cu sup (-1~) -K sup (-2). The critical current density at 77K and H=O exceeds 1100 A/cm sup 2.