Cation nonstoichiometry in (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+δ

Abstract

X-ray lattice parameter measurements of the (Bi, Pb) 2- x Sr 2- y Ca 2- z Cu 3O 10+δ system show that a continuously varying solid-solution cation nonstoichiometry exists within -0.1< x<0.1, 0< y<0.3, and 0< z<0.3. However, the system cannot incorporate any defect at its Cu site. The oxygen content determined by titration decreases linearly with increasing cation-vacancy concentration. The critical temperature, T c, shows a maximum value at the stoichiometric cation composition and decreases to a lower constant value across the nonstoichiometric composition region with increasing alkaline-earth deficiency. Flux pinning in this system is increased by the cation-vacancy concentration only in the low-temperature range, while it decreased in the high-temperature range. The flux-pinning behavior is discussed in view of its two-dimensionality in the superconductivity for this system.