Effect of pulling rate on transport property of directionally solidified Y123 superconducting fiber

The Y123 fibers with 0.5 mm in diameter were directionally solidified and the transport Jc properties were evaluated. The continuously grown Y123 crystals were obtained at high pulling rates up to 10 mm/h. The maximum transport Jc value of 1 × 105 A/cm2 (Ic = 134 A) was achieved in the sample grown at pulling rate of 6 mm/h. Such the high Jc value would be the result of better crystal orientation at high pulling rates, although Jc was decreased in the samples grown over 6 mm/h due to sub-domain structure that would be induced during the high speed growth. The two step growth process was tried to improve microstructure preserving the crystal orientation. The Jc values of the two step grown samples were disappointingly lower than those fabricated at the constant pulling rate, since the continuous growth structure was broken after the sudden change of pulling rate. The gradual change of pulling rate may be required to maintain the continuous growth.