Superconducting joints are essential for iron-based superconductor's applications in future. In this study, a process for fabricating superconducting joints between Sr1-xKxFe2As2 (Sr-122) tapes is developed for the first time. The Ag sheath was peeled off from one side of each sample. The exposed superconducting parts of the two tapes were joined and wrapped again with Ag foil. The diffusion bonding of the iron-based superconducting joint was achieved by hot-pressing process in Argon atmosphere. The superconducting properties, microstructures and the elements distribution of the joint regions had been investigated. The pressure and pressing times were optimized in order to enhance the transport current of the joints. At 4.2 K and 10 T, a transport critical current Ic of 57 A for the joint was obtained, which is approximately 63.3% of the current capacity of the tapes themselves. Furthermore, the joint resistances dV/dI were estimated from the V-I curve of the joints and the calculated joint resistances values are below 10 -9 Ω. These results demonstrate that the hot pressing was useful for fabricating the superconducting joint samples.

Ag-sheathed CaKFe4As4 superconducting tapes have been fabricated via the ex-situ powder-in-tube method. Thermal and X-ray diffraction analyses suggest that the CaKFe4As4 phase is unstable at high temperatures. It decomposes into the CaAgAs phase which reacts strongly with the silver sheath. We therefore sintered the tape at 500 °C and obtain a transport critical current density Jc(4.2 K, 0 T)~ 2.7 × 10 4 A/cm 2 . The pinning potential derived from magnetoresistance measurements is one order of magnitude lower than that of the (Ba/Sr)1-xKxFe2As2 tapes. Combining with the scanning electron microscopy and magneto-optical imaging results, we suggest that bad connectivity between superconducting grains caused by the low sintering temperature is the main factor responsible for the low Jc. However, this system is still a promising candidate for superconducting wires and tapes if we further optimize the post-annealing process to achieve better grain connectivity.

Superconducting joints are one of the crucial components to make Sr1−xKxFe2As2 (Sr-122) superconducting wires or tapes successful for future high-field, high-homogeneity magnetic application. In this paper, the hot-pressing process for an iron-based superconducting joint of Sr-122 tapes was optimized. The microstructures, superconducting properties and element distribution in the connection areas were researched. The transport properties of the iron-based superconducting joints were enhanced by prolonging the holding time at high pressure, which prevents potassium loss in the iron-based superconducting joint. The best transport critical current that was achieved was 57 A at 4.2 K and 10 T; meanwhile, the critical current ratio (CCR = Icjoint/Icnon-joint) of the joint was realized to be 63.3%, which is the highest value of an iron-based superconducting joint reported so far. These results clearly demonstrate that iron-based superconductors are very promising for high-field magnet applications.