Radial inhomogeneities induced by fiber diameter in electrically assisted LFZ growth of Bi-2212

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 Bix(Sr,Ca)yOz phase crystallizes preferentially from the melt in the wider fibers, acting as obstacles to the current flux.