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.