Whereas porous polycrystalline samples of MgB2 could be synthesized from B powder, it was demonstrated that dense wires could be prepared by exposing B filaments to Mg vapor. The resultant wires had a diameter of 160μm, were better than 80% dense, and exhibited full χ = -1/4π shielding in the superconducting state. Temperature-dependent resistivity measurements indicated that MgB2 was a highly conducting metal in the normal state with a conductivity, at 40K, of 0.38μΩcm. By using this value, an electronic mean-free path of about 60nm was estimated; indicating that the wires were well within the clean limit. The TC, HC2(T) and JC data indicated that MgB2 had comparable or better superconducting properties in the dense wire form than it had as a sintered pellet.

Superconductivity in Dense MgB2 Wires. P.C.Canfield, D.K.Finnemore, S.L.Budko, J.E.Ostenson, G.Lapertot, C.E.Cunningham, C.Petrovic: Physical Review Letters, 2001, 86[11], 2423-6