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MgB2 coated superconducting tapes with high critical current densities fabricated by hybrid physical-chemical vapor deposition

The MgB2 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 MgB2/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 (Tc) ranging between 36 and 38 K with superconducting transition width (\DeltaTc) of about 0.3-0.6 K. The highest critical current density (Jc) of 1.34 \times 105 A/cm2 at 5 K under 3 T is obtained for the MgB2/Cu tape grown at 460^{\circ}C. To further improve the flux pinning property of MgB2 tapes, SiC is coated as an impurity layer on the Cu tape. In contrast to pure MgB2/Cu tapes, the MgB2 on SiC-coated Cu tapes exhibited opposite trend in the dependence of Jc with growth temperature. The improved flux pinning by the additional defects created by SiC-impurity layer along with the MgB2 grain boundaries lead to strong improvement in Jc for the MgB2/SiC/Cu tapes. The MgB2/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 Jc values over the wide field range for MgB2/Hastelloy tapes than the previously reported data on other metallic substrates, such as Cu, SS, and Nb. The Jc values of Jc(20 K, 0 T) \sim5.8 \times 106 A/cm2 and Jc(20 K, 1.5 T) ~2.4 \times 105 A/cm2 is obtained for the 2-\mum-thick MgB2/Hastelloy tape. This paper will review the merits of coated conductor approach along with the HPCVD technique to fabricate MgB2 conductors with high Tc and Jc values which are useful for large scale applications.