Cation Deficiency in Bi2(Sr,Ca)3Cu2O8+d

Abstract

X‐ray lattice parameter measurements of the Bi2‐x (Sr,Ca)3‐yCu2‐zO8+d system show that a continuously varying solid‐solution cation nonstoichiometry exists within the overall composition ranges x < 0.32, ‐0.2 < y < 0.32, and z < 0.25. A modulated structure along the b axis remains present over these composition ranges. Defects introduced by cation deficiency have been clarified to be vacancies by density measurements. The oxygen content determined by titration decreases proportionately with increasing cation vacancy concentrations. In Bi‐deficient compositions, the interstitial oxygen ion concentration decreased and the oxygen vacancy concentration increased with increasing concentration of Bi vacancies. The critical temperature, Tc, shows a maximum value at the stoichiometric cation composition and decreases to a slightly lower (5 to 10 K) constant value across the nonstoichiometric composition region with both increasing alkaline‐earth and Cu deficiency.