Transport critical currents in the iron pnictide superconducting wires prepared by the ex situ PIT method

The discovery of iron-based superconductors, the first non-cuprate family of superconductors with Tc above 40 K, has stimulated enormous interest in the field of superconductivity since last year. This remarkable discovery not only offers the opportunity to study the origin of superconductivity, but also opens up new possibilities of application. One of the most fascinating and useful properties of superconductors is the ability to carry electrical current with zero resistance. Here, we report the successful fabrication of dense Sr0.6K0.4Fe2As2 superconducting wires using the ex situ powder-in-tube (PIT) method and demonstrate a transport Jc of 3750 A cm-2 at 4.2 K. The connectivity of grains was improved upon doping (Ag or Pb) and the transport property of Sr0.6K0.4Fe2As2 wires was enhanced for a lead-doped sample, especially in low fields, to a best Ic of 37.5 A. Our results suggest that grain boundary properties require much greater attention when looking for applications of the high-Tc iron-based superconductors.