Investigation of Jc-Suppressing Factors in Flat-Rolled Sr0.6K0.4Fe2As2/Fe Tapes Via Microstructure Analysis

Pnictide superconductors will be very promising for applications if wires with high critical current density J(c) can allow reel-to-reel large-scale fabrication at low costs. To understand the mechanism(s) that limited Jc in flat-rolled Sr0.6K0.4Fe2As2 (Sr122) tapes, microstructure analysis has been considered the most direct and efficient way. Here, we report on high-resolution microstructure imaging and analysis on Fe-sheathed flat-rolled Sr122 tapes, which have a J(c) as high as 2.3 x 10(4) A/cm(2) at 10 T and 4.2 K. The overlapping nature of the Sr122 plates was clearly observed. Transmission electron microscopy/scanning transmission electronmicroscopy analysis showed that, besides the cracks formed during the fabrication process, the SrO2 phase and cavities caused by the inhomogeneously dispersed Sr and K are the other important factors suppressing J(c). The wetting phase FeAs at the grain boundaries can be partially substituted by Sn in Sn-added samples. Our findings provide insights that pave the way to further enhance the critical current of the rolled 122 tapes up to the practical level.