Single-phase 60-K bulk superconductor in annealed Ba2YCu307(0.3<<0.4) with correlated oxygen vacancies in the Cu-O chains

Employing a gettered annealing technique, we have prepared homogeneous polycrystalline samples of oxygen-deficient Ba2YCu3O7 for 00.7. Measurements of resistive Tc, resistivity, magnetization, and lattice parameter indicate that a distinct bulk superconducting phase with a Tc of 60 K occurs in the range of 0.3<<0.4. This phase displays partial ordering of oxygen vacancies in the Cu-O chains as found by electron diffraction studies.