MgB 2 coated superconducting tapes with high critical current densities fabricated by hybrid physical–chemical vapor deposition

Abstract

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 (Δ T 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.