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

Abstract

The application of an electric current of 200 mA through the molten zone of BSCCOsuperconducting fibres during laser floating zone processing constitutes an upgradefor improving the grain alignment. When a direct electric current (positivelypolarized fibre) passes through the solidification interface, the solidification conditionsapproach equilibrium, favouring the development of a higher amount of 2212 and14/24 stable phases. The new electrically assisted laser floating zone (EALFZ) technique alsoimproves the 2223 phase formation in fibres heat treated at high temperatures(860 °C).However, the 2223 crystals grow perpendicularly to the fibre axis at the interface between the 2212and 14/24 phases, crossing the crystals of the main phase responsible for the current transport, cancellingthe alignment effect. The resultant current density and critical temperature values wereJc77 K = 230 A cm−2 and Tc = 85 K, respectively. When a lower heat treatment temperature was accomplished(820 °C), the 2223 transverse crystals do not develop and a higher current density value ofJc77 K = 510 A cm−2 was achieved, although with a critical temperature ofTc = 90 K.