Development of Ca/K-1144 IBS Wires With Composite Cu/Ta Sheaths

Ca/K-1144 compounds constitute promising materials to be exploited for the fabrication of Iron Based Superconductors (IBSC) wires via the Powder in Tube (PIT) method thanks to the high critical currents observed in single crystals coupled to the simple and robust chemical composition. The production of Ca/K-1144 wires has been however hindered by the reactivity of Ca with Ag, the common choice for sheath materials in IBSC wires. In our recent work, we demonstrated the potentiality of composite Cu/Ta sheaths to be adopted for these kinds of applications. In this work, we show the effect of the variation of sintering temperature and mechanical processing on the morpho-structural and superconducting properties of wires processed through this combination of materials. While critical currents are still to be improved, compared to state of the art 122-Ag wires, with evident margins for what concerns both the synthesis step and the wire production process, the results show how sintering temperature can be raised up to 900 °C. The intrinsic fragility of pure Ta observed during the wire processing is proposed to be mitigated by tailoring the sheath dimensions or the Ta barrier chemical composition.