Improved Superconducting Properties for Multifilament Graphene-Coated Nb Addition MgB 2 Wires by an Internal Mg Diffusion Process

A novel method is presented for the production of the 6 + 1 filament MgB 2 wires using internal Mg diffusion (IMD) process. For the MgB 2 long wire with 1.4-mm diameter produced by graphene-coated Nb addition, the critical current ( I c ) is about 1000 A at 4 T and 4.2 K, which is 2.5 times higher than that of the undoped sample. The increased I c is attributed to the enhanced flux pinning force and improved grain connectivity. The obtained results show that graphene-coated Nb addition MgB 2 wires have excellent superconductivity and mechanical property compared with the conventional PIT wires in practical application.