Effects of core density and impurities on the critical current density of CaKFe4As4 superconducting tapes

CaKFe4As4 superconducting tapes are fabricated via different techniques to enhance grain connectivity. The critical current density, J c, increases exponentially with the Vickers hardness of the superconducting core. The J c (4.2 K, 10 T) of the hot isostatic pressed Cu/Ag-sheathed tape reaches 2.2 × 104 A cm−2, while that of the stainless steel/Ag-sheathed tapes surpasses 104 A cm−2. However, silver infiltrates from the sheath far into the center of the superconducting core and reacts with the CaKFe4As4 phase, which has significant ramifications for the transport current. We suggest that CaKFe4As4 has great potential if we can realize stable coexistence between the superconducting core and the sheath.