Synthesis and processing of (Hg,Pb)₁Ba₂Ca₂Cu₃O_y superconductors

Synthesis and processing of bulk (Hg,Pb)Ba₂Ca₂Cu₃O_y (HgPb1223) superconductor using commercial BaCaCuO precursor powders is reported. HgPb1223 is shown to form over a wide range of temperatures, 750-880°C. The micro structure and intergrain connectivity of samples depends strongly on heat treatment and Hg-pressure during synthesis. Use of an external Hg-source during the reaction improves the density of the HgPb1223 products. The chemical nature of the external Hg-source changes the Hg-pressure and influences melting characteristics and grain growth. CaHgO₂ is shown to be a particularly effective external Hg-source for producing dense HgPb1223 materials with improved grain growth and texture. Micro structure of HgPb1223 synthesized using CaHgO₂ as the external Hg-source is characterized by large colonies of well-aligned superconducting grains. As-synthesized HgPb1223 samples were superconducting with T_c values in the range 132-134 K without post annealing in oxygen or argon. Phase purity and microstructural characteristics are correlated with magnetization measurements.