Structure and Superconducting Properties of Single-Filamentary MgB2/Nb,Cu Composite Doped with Carbon Nanotubes

The present study investigates the effect of carbon doping on the structure and superconducting properties of MgB2-based composites fabricated by powder-in-tube ex-situ method using carbon nanotubes as carbon sources. It is demonstrated that carbon is incorporated into the MgB2 lattice, substituting for boron, which results in a decrease in the lattice parameter. The lattice defects caused by doping have no appreciable effect on the dislocation structure formed in the composite in the course of cold drawing and annealing. Thin interlayers of NbB at grain boundaries are found, indicating the diffusion of niobium into the superconductive core.