coated superconducting tapes with high critical current densities fabricated by hybrid physicalechemical vapor deposition

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 $460-520^{\circ}C$ by using hybrid physicalechemical vapor deposition (HPCVD) technique. The tapes exhibited the critical temperatures (Tc) ranging between 36 and 38 K with superconducting transition width (${\Delta}Tc$) of about 0.3e0.6 K. The highest critical current density (Jc) of $1.34{\times}10^5\;A/cm^2$ 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 $MgB_2$ 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 Jc 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 Jc for the $MgB_2$/SiC/Cu tapes. The MgB2/Hastelloy superconducting tapes fabricated at a temperature of $520^{\circ}C$ 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) ~$5.8{\times}10^6\;A/cm^2$ and Jc(20 K, 1.5 T) ~$2.4{\times}10^5\;A/cm^2$ is obtained for the 2-${\mu}m$-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 Tc and Jc values which are useful for large scale applications.