Superconductivity of Bi₂Sr₂Ca_1-xY_xCu₂O_y Synthesized by Polymelized Complex Technique

Abstract

Superconducting Bi-Sr-Ca-Y-Cu-O ceramics have been synthe-sized by the polymerized complex method at the Bi₂Sr₂Ca_1-xY_xCu₂O_y (0 ≤ x ≤ 0.4) compositions, and the dependence of the superconducting transition on the hole concentration was studied. The onset temperature of the superconducting transition T_c(onset) was carefully measured in terms of complex susceptibility. The onset temperature is enhanced as x increases up to x = 0.1 and then decreases as x further increases. Wet chemical analyses were carried out to determine the average charges of Bi and Cu ions. To interpret the results, we propose that the mixed valence of Bi⁺⁵ and Bi⁺³ acts as a charge reservoir for the Cu0₂ planes.