SYNTHESIS AND PROCESSING OF (HG,PB)(1)BA2CA2CU3OY SUPERCONDUCTORS

Synthesis and processing of bulk (Hg,Pb)Ba2Ca2Cu3Oy (HgPb1223) superco nductor using commercial BaCaCuO precursor powders is reported. HgPb12 23 is shown to form over a wide range of temperatures, 750-880 degrees C. The microstructure 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 Hg Pb 1223 products. The chemical nature of the external Hg-source change s the Hg-pressure and influences melting characteristics and grain gro wth. CaHgO2 is shown to be a particularly effective external Hg-source for producing dense HgPb1223 materials with improved grain growth and texture. Microstructure of HgPb1223 synthesized using CaHgO2 as the e xternal Hg-source is characterized by large colonies of well-aligned s uperconducting grains. As-synthesized HgPb1223 samples were supercondu cting 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. (C) 1998 Elsevier Science B.V.