Crystal structure and superconductivity controlled by cation substitution and oxygen annealing in y_1-xca_xba₂cu₃o_yand yba_2-xla_xcu₃o_y

The effects of Ca²⁺substitution for Y³⁺and La³⁺substitution for Ba²⁺in YBa₂Cu₃O₇on the structural and superconducting properties were studied to control the average copper charge. Single-phase tripled perovskites were obtained for 0≦x≦0.2 and 0≦x≦1.0 for Ca and La doped series, respectively. A slight decrease of T_cwith increasing x was found for small x values for both kinds of substituted specimens prepared by furnace cooling in air. Oxygen annealing experiments were also carried out. These suggested that the superconduction in the Y-Ba-Cu-O system cannot be interpreted only by oxygen content or average copper charge.