Synthesis and processing of MgB2 powders and wires

Sintered powders and wires of superconducting MgB2 have been fabricated under a variety of conditions in order to determine details of the diffusion of the Mg into B and to study the types of defects that arise during growth. For samples prepared by exposure of boron to Mg vapor at 950 degreesC, the conversion of particles of less than 100 mum size to MgB2 is complete in about 2 h. The lattice parameters of the MgB2 phase determined from X-ray are independent of the starting stoichiometry and the time of reaction. Wire segments of MgB2 with very little porosity have been produced by reacting 141 mum diameter boron fibers in an atmosphere of excess Mg vapor at 950 degreesC. Defects in the reacted fibers are predominantly voids left as the boron is converted to MgB2. Published by Elsevier Science B.V.