Investigation of $J_{c}$-Suppressing Factors in Flat-Rolled $\hbox{Sr}_{0.6}\hbox{K}_{0.4}\hbox{Fe}_{2}\hbox{As}_{2}/\hbox{Fe}$ 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 J
_c
in flat-rolled Sr
_0.6
K
_0.4
Fe
₂
As
₂
(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 × 104 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 electron microscopy analysis showed that, besides the cracks formed during the fabrication process, the SrO
₂
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.