Enhancement of critical current density in HgBa2Ca2Cu3O8+δ superconductor doped by Sb

Antimony-free Hg-1223 and antimony-doped (Hg0.95Sn0.05)-1223 superconductors were synthesized in sealed silica tubes by the solid state reaction method. The precursor can be prepared in air. A series of experimental results obtained from the Sb-doped and Sb-free superconductors by X-ray diffraction, scanning electron microscopy (SEM), thermogravity analysis, resistance measurements and AC susceptibility measurement techniques shows that a small addition of Sb increases the volume fraction of the Hg(Sb)-1223 superconducting phase and enhances the intergrain critical current density J(c), as well as the thermal stability of this superconducting phase. The T-c of the Sb-doped sample decreases by about 4 K as compared with that of the pure Hg-1223 superconductor. SEM observation shows many plate-like superconducting grains which seem to be more dense in their packing for the Sb-doped sample than in the Sb-free sample. The enhancement of current density J(c) is due to the Sb doping which improves the coupling status for their intergrains. These grains modify the characteristics and the nature of superconducting grain boundaries. Furthermore, an orthorhombic insulating phase, with a = 1.6603 nm, b = 1.0618 nm, and c = 0.87575 nm, was found to appear in the (Hg0.70Sb0.30)-1223 sample. (C) 1998 Published by Elsevier Science B.V. All rights reserved.