Influence of the preparation process on microstructure, critical current density and T/sub c/ of MgB/sub 2/ powder-in-tube wires

MgB/sub 2/ wires and tapes suffer from a limitation of the transport current densities, especially at low field, due to an unsufficient thermal stabilization caused by hot spots from a nonhomogeneous microstructure, the presence of secondary phases and voids. For the preparation of MgB/sub 2/ wires and tapes two different precursor routes, using MgB/sub 2/ (ex-situ process) or Mg + B (in-situ process) are applied. The in-situ approach allows variation of many parameters in the wire preparation and the improvement of this approach is the central topic of this paper. We present an improved in-situ approach, the characterization of the filament microstructure, effects from stoichiometry and the corresponding superconducting properties. The transport current capability of such in-situ wires could be improved to the level of the reference ex-situ wires.