Large transport critical currents of powder-in-tube Sr0.6K0.4Fe2As2/Ag superconducting wires and tapes

We report the achievement of transport critical currents in Sr0.6K0.4Fe2As2 wires and tapes with a T-c = 34 K. The wires and tapes were fabricated through an in situ powder-in-tube process. Silver was used as a chemical addition as well as a sheath material. All the wire and tape samples have shown the ability to transport superconducting current. Critical current density J(c) was enhanced upon silver addition, and at 4.2 K, a largest J(c) of similar to 1200 A/cm(2) (I-c = 9 A) was achieved for 20% silver added tapes, which is the highest in iron-based wires and tapes so far. The J(c) is almost field independent between I T and 10 T, exhibiting a strong vortex pinning. Such a high transport critical current density is attributed to the weak reaction between the silver sheath and the superconducting core, as well as an improved connectivity between grains. We also identify a weak-link behavior from the apparent drop of J(c) at low fields and a hysteretic phenomenon. Finally, we found that compared to Fe, Ta and Nb tubes, Ag was the best sheath material for the fabrication of high-performance 122 type pnictide wires and tapes. (C) 2009 Elsevier B.V. All rights reserved.