ENHANCEMENT OF CRITICAL-CURRENT DENSITY IN HGBA2CA2CU3O8+DELTA SUPERCONDUCTOR DOPED BY SB

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