High volume fractions of the n=2 and n=3 members of a cuprate system of general formula ${\mathrm{Hg}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pb}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Ca}}_{\mathit{n}\mathrm{-}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{2\mathit{n}\mathrm{-}2+\mathrm{\delta }}$ (with an average value of x at 0.33) have been synthesized via a relatively facile process using low oxygen pressures. For as-synthesized n=3 (Hg,Pb-1:2:2:3) bulk superconducting critical temperatures (${\mathit{T}}_{\mathit{c}}$) of up to 133 K have been observed. For n=2 (Hg,Pb-1:2:1:2), which is obtained with some rare-earth-ion substitution at the calcium site, ${\mathit{T}}_{\mathit{c}}$ is 125 K after annealing in a reducing atmosphere. High-resolution lattice imaging coupled with structural simulations show that the Pb ions go into the Hg layer, leading to a chemical pressure-induced compositional modulation in this plane. Strong flux pinning and an irreversibility field of 1 T at 80 K are observed for Hg,Pb-1:2:2:3.

• Received 27 December 1993

DOI:https://doi.org/10.1103/PhysRevB.49.12322