Modulation-free bismuth-lead cuprate superconductors : BiPbSr1+x L1-x Cu06 and BiPbSr2 Y1-x CaxCu2O8

Abstract

Modulation-free BiPbSrLCuO6 (L = La, Pr, Nd) and BiPbSr2YCu2O8, which are isotypic with the n = 1 and 2 members of the Bi2Sr2Ca(n-1)Cu(n)O2n+4 family, have been prepared and characterized. These parent compounds are nonsuperconducting, but when doped with holes by substitution chemistry give modulation-free superconducting cuprates of the general formulas BiPbSr(1+x)L(1-x)CuO6 and BiPbSr2Y(1-x)Ca(x)Cu2O8, exhibiting maximum T(c)'s of 24 and 85 K, respectively. Significantly, the hole concentration at the maximum T(c) is 0.12 in the cuprate family with a single Cu-O layer and 0.22 in that with two Cu-O layers.