Microscopic origin of highly enhanced supercurrent in 122 pnictide superconductor

Highlights: • The mechanisms for the remarkable enhancement of supercurrent have been revealed. • Hot pressing promotes low-angle grain boundaries and texturing of the crystals. • Dislocation lines acting as pinning centres and increasing critical current density. • Grain boundary engineering is an effective way to improve critical current density. By a combination of microstructure analysis techniques, we reveal the structural origin of the extremely high supercurrent (up to the practical level of 0.1 MA/cm² at 10 T, 4.2 K) in Sr_0.6K_0.4Fe₂As₂ (122) tape. Transmission Kikuchi diffraction analysis reveals that hot pressing promotes a very high fraction of low-angle grain boundaries and texturing of the crystals, which is beneficial for the intergrain physical properties. Moreover, the unique characteristics of low-angle grain boundaries favor both long-range dislocations and short-range dislocations that totally change the pinning mechanism of the bulk 122 system. These defects combined with the grain texturing are not only effective for pinning vortices in the superconducting state, but also improve inter-granular supercurrent degradation, leading to substantially enhanced supercurrent over a wide range of magnetic fields.