Oxygen stoichiometry, superconductivity and normal-state properties of YBa2Cu3O(7-delta)

Work presented so far on the dependence of both superconducting and normal- state properties on oxygen stoichiometry in the new high-temperature oxide superconductors has considered only the value of delta in YBa2Cu3O(7- delta). Data are presented here that indicate the issue to be considerably more interesting and complex, and it is proposed that the microscopic variables thus far not considered include the distribution of oxygen over the available sets of sites in the structure, with that distribution strongly dependent on synthetic conditions. In addition to the dependence of the bulk transition temperature, normal-state resistivity and crystallographic symmetry on the microscopic distribution, the magnitude of the magnetic susceptibility in the normal state is found to be strongly affected by the microscopic state of the oxygen subsystem. The existence of a single-phase 60-K bulk superconductor at stoichiometry YBa2Cu3O(6.6- 6.7) is also reported. (C.D.)