Effect of chemical inhomogeneity in bismuth-based copper oxide superconductors

We examine the effect on the superconducting transition temperature (T-c) of chemical inhomogeneities in Bi2Sr2CuO6+delta and Bi2Sr2CaCu2O8+delta single crystals. Cation disorder at the Sr crystallographic site is inherent in these materials and strongly affects the value of T-c. Partial substitution of Sr by Ln (Ln = La, Pr, Nd, Sm, Eu, Gd, and Bi) in Bi(2)Sr(1.6)Ln(0.4)CuO(6+delta) results in a monotonic decrease of T-c with increasing ionic radius mismatch. By minimizing Sr site disorder at the expense of Ca site disorder, we demonstrate that the T-c of Bi2Sr2CaCu2O8+delta can be increased to 96 K. Based on these results we discuss the effects of chemical inhomogeneity in other bulk high-temperature superconductors.