Syntheses and neutron powder diffraction studies of the superconductor HgBa2Ca2Cu3O8+delta by Pb substitution

Substitution of Pb for Hg was performed in the Hg based 1223 phase HgBa2Ca2Cu3O8+delta a (T-c similar to 135 K), resulting in an increase of the superconducting transition temperature to T-c(dia) = 143 K for samples with a nominal composition of Hg0.7Pb0.3Ba2Ca2Cu3O8+delta. The crystal structure of this solid solution has been investigated by neutron powder diffraction (NPD) and synchrotron X-ray diffraction (SXRD) techniques at room temperature (RT). The compound has the same crystal structure as Hg-1223 with the space group P4/mmm and lattice parameters a = 3.8457(1) Angstrom and c = 15.8252(7) Angstrom. Rietveld analysis results indicate that Hg is partially replaced by Pb, and the oxygen content, delta, is 0.450(2). The lattice parameter changes resulting from the Pb substitution are too small to account for the T-c change mimicking the effect of pressure.