The effect of current direction on superconducting properties of BSCCO fibres grown by an electrically assisted laser floating zone process

The application of an electric current of 200 mA through the molten zone of BSCCO superconducting fibres during laser floating zone processing constitutes an upgrade for improving the grain alignment. When a direct electric current (positively polarized fibre) passes through the solidification interface, the solidification conditions approach equilibrium, favouring the development of a higher amount of 2212 and 14/24 stable phases. The new electrically assisted laser floating zone (EALFZ) technique also improves the 2223 phase formation in fibres heat treated at high temperatures (860 deg. C). However, the 2223 crystals grow perpendicularly to the fibre axis at the interface between the 2212 and 14/24 phases, crossing the crystals of the main phase responsible for the current transport, cancelling the alignment effect. The resultant current density and critical temperature values were Jc77K = 230 A cm-2 and Tc = 85 K, respectively. When a lower heat treatment temperature was accomplished (820 deg. C), the 2223 transverse crystals do not develop and a higher current density value of Jc77K = 510 A cm-2 was achieved, although with a critical temperature of Tc = 90 K