Radial Inhomogeneities Induced By Fiber Diameter In Electrically Assisted Lfz Growth Of Bi-2212

摘要

Superconducting polycrystalline BSCCO fibers of 2:2:1:2 nominal composition were grown by the electrically assisted laser floating zone (EALFZ) technique. An electric current density of 2.1 A cm~(-2) was applied through the solid/liquid (S/L) interface. A net effect of the fiber diameter on the as-grown microstructure and on the final superconducting properties is observed. A higher critical current density (～2520 A cm~(-2)) results for the thinner fibers (Φ = 1.7 mm) comparing to the value (～1065 A cm~(-2)) found for the wider ones (Φ = 2.5 mm). The steep axial thermal gradient at the S/L interface in the thinner fibers is responsible for its superior texture degree, a crucial parameter for improved current transport properties. Moreover, a Cu-free Bi_χ(Sr,Ca)_yO_z phase crystallizes preferentially from the melt in the wider fibers, acting as obstacles to the current flux.