SUPERCONDUCTIVITY ABOVE 130 K IN THE HG-PB-BA-CA-CU-O SYSTEM

High volume fractions of the n=2 and n=3 members of a cuprate system of general formula Hg1-xPbxBa2Can-1CunO2n-2+ (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 (Tc) 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, Tc 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.