MgB_2 coated superconducting tapes with high critical current densities fabricated by hybrid physical-chemical vapor deposition

摘要

The MgB_2 coated superconducting tapes have been fabricated on textured Cu (0 0 1) and polycrystalline Hastelloy tapes using coated conductor technique, which has been developed for the second generation high temperature superconducting wires. The MgB_2/Cu tapes were fabricated over a wide temperature range of 460-520 °C by using hybrid physical-chemical vapor deposition (HPCVD) technique. The tapes exhibited the critical temperatures (T_c) ranging between 36 and 38 K with superconducting transition width (ΔT_c) of about 0.3-0.6 K. The highest critical current density (J_c) of 1.34 × 10~5 A/cm~2 at 5 K under 3 T is obtained for the MgB_2/Cu tape grown at 460 °C. To further improve the flux pinning property of MgB_2 tapes, SiC is coated as an impurity layer on the Cu tape. In contrast to pure MgB _2/Cu tapes, the MgB_2 on SiC-coated Cu tapes exhibited opposite trend in the dependence of J_c with growth temperature. The improved flux pinning by the additional defects created by SiC-impurity layer along with the MgB_2 grain boundaries lead to strong improvement in J_c for the MgB_2/SiC/Cu tapes. The MgB_2/ Hastelloy superconducting tapes fabricated at a temperature of 520 °C showed the critical temperatures ranging between 38.5 and 39.6 K. We obtained much higher J_c values over the wide field range for MgB _2/Hastelloy tapes than the previously reported data on other metallic substrates, such as Cu, SS, and Nb. The J_c values of J _c(20 K, 0 T) ～5.8 × 10~6 A/cm~2 and J_c(20 K, 1.5 T) ～2.4 × 10~5 A/cm~2 is obtained for the 2-μm-thick MgB_2/Hastelloy tape. This paper will review the merits of coated conductor approach along with the HPCVD technique to fabricate MgB_2 conductors with high T_c and J_c values which are useful for large scale applications.