  From the application point of view, large critical current densities Jc (H)
for superconducting wires are required, preferably for magnetic fields higher
than 5 T. Here we show that strong c-axis textured Sr1-xKxFe2As2 tapes with
nearly isotropic transport Jc were fabricated by an ex-situ powder-in-tube
(PIT) process. At 4.2 K, the Jc values show extremely weak magnetic field
dependence and reach high values of 1.7x10^4 A/cm^2 at 10 T and 1.4x10^4 A/cm^2
at 14 T, respectively, these values are by far the highest ever reported for
iron based wires and approach the Jc level desired for practical applications.
Transmission electron microscopy investigations revealed that amorphous oxide
layers at grain boundaries were significantly reduced by Sn addition which
resulted in greatly improved intergranular connectivity. Our results
demonstrated the strong potential of using iron based superconductors for high
field applications.
