Crystal Structure and Superconductivity Controlled by Cation Substitution and Oxygen Annealing in Y_1-xCa_xBa₂Cu₃O_y and YBa_2-xLa_xCu₃O_y

Abstract

The effects of Ca 2+ substitution for Y 3+ and La 3+ substitution for Ba 2+ in YBa 2 Cu 3 O 7 on 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 c with 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.