Enhancement of superconductivity in LFZ-grown BSCCO fibres by steeper axial temperature gradients

Laser floating zone (LFZ) method was employed to grow superconducting polycrystalline Bi–Sr–Ca–Cu–O fibres of 2:2:1:2 nominal composition with two different diameters (1.75 and 2.50 mm). The temperature profile at the solid/liquid interface was calculated along the fibre radii from estimations of the heat transfer coefficient and thermal conductivity of the fibres. Values of temperature gradient G = 3.17 × 105 K m−1 and G = 2.65 × 105 K m−1 at the fibre centre were obtained for the thinner and the thicker fibres, respectively. Growth under a steep temperature gradient has significant consequences on the microstructure of the thinner fibres: an improved texture and the absence of the copper-free Bix(Sr,Ca)yOz secondary phase. These features lead to the superior transport properties of the thinner fibres that present a higher value of critical current density (JC = 2200 A cm−2) than the wider ones (JC = 1400 A cm−2).