MgB2 coated conductors directly grown on flexible metallic Hastelloy tapes by hybrid physical–chemical vapor deposition

• MgB2 with superior superconducting properties were grown directly on Hastelloy tapes.
• Hastelloy tape was found a better substrate to avoid chemical reactions with MgB2.
• The Jc, Fp, Hc2, and Hirr were increased as the growth temperature decreased.
• Further improvement in Jc, Fp, Hc2, and Hirr would be expected by making MgB2 dirtier.

MgB2 coated conductors (CCs), which can avoid the low packing density problem of powder-in-tube (PIT) processed wires, can be a realistic solution for practical engineering applications. Here we report on the superior superconducting properties of MgB2 CCs grown directly on the flexible metallic Hastelloy tapes without any buffer layer at various deposition temperatures from 520 to 600 °C by using hybrid physical–chemical vapor deposition (HPCVD) technique. The superconducting transition temperatures (Tc) are in the range of 38.5–39.4 K, comparable to bulk samples and high quality thin films. Clear (101) and (002) reflection peaks of MgB2 are observed in the X-ray diffraction patterns without any indication of chemical reaction between MgB2 and Hastelloy tapes. From scanning electron microscopy, it was found that connection between MgB2 grains and voids strongly depend on the growth temperature. A systematic increase in the flux pinning force density and thereby the critical current density with decreasing growth temperature was observed for the MgB2 CCs. The critical current density (Jc) of Jc(5 K, 0 T) ∼107 A/cm2 and Jc(5 K, 2.5 T) ∼105 A/cm2 has been obtained for the sample fabricated at a low growth temperature of 520 °C. The enhanced Jc (H) behavior can be understood on the basis of the variation in the microstructure of MgB2 CCs with growth temperature.