Influence of Amorphous Carbon Doping on Superconductivity of MgB2/Nb/Cu Wires

The effects of amorphous carbon doping on superconducting properties of MgB2/Nb/Cu wires fabricated by the in-situ powder-in-tube (PIT) method have been investigated. Using Nb as the barrier and Cu as the stabilizer, the MgB2 wires were fabricated by cold drawing. The wires of MgB2-xCx (x = 0.0, 0.05, 0.08, 0.10, 0.15) have been investigated to realize the effect of amorphous carbon doping on the phase formation, microstructure and superconducting properties. Characterization of MgB2/Nb/Cu wires was carried out using XRD, SQUID, SEM/EDS, and I-c measurements. XRD result shows that the high purity MgB2 phase is acquired after heat-treatment at 700 degrees C. The microstructure observation for wires shows that the MgB2/Nb/Cu wires have better grain connectivity after doping amorphous carbon, and Energy Dispersive X-ray (EDS) analysis confirms the uniform distribution of carbon in the MgB2 superconducting phase. The critical current density (J(c)) of wires was measured in different magnetic fields by a standard four probes method, and the transport J(c) values as high as 1.4 x 10(5) A/cm(2) (4.2 K, 5 T) and 3.3x 10(4) A/cm(2) (4.2 K, 10 T) have been achieved.