Crystal Structure and Superconductivity Controlled by Cation Substitution and Oxygen Annealing in Y1-xCaxBa2Cu3Oy and YBa2-xLaxCu3Oy

Abstract
The effects of Ca2+ substitution for Y3+ and La3+ substitution for Ba2+ in YBa2Cu3O7 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.