From the application point of view, large critical current densities J c (H) for superconducting wires are required, preferably for magnetic fields higher than 5 T. Here we show that strong c-axis textured Sr 1-xKxFe2As2 tapes with nearly isotropic transport J c were fabricated by an ex-situ powder-in-tube (PIT) process. At 4.2 K, the J c values show extremely weak magnetic field dependence and reach high values of 1.7×104 A/cm2 at 10 T and 1.4×104 A/cm2 at 14 T, respectively, these values are by far the highest ever reported for iron based wires and approach the J c 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.
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