High tolerance of the superconducting current to large grain boundary angles in potassium-doped BaFe₂As₂

Superconducting magnets based on high-temperature superconductors (HTSs) have become critical components in cutting-edge technologies such as advanced medical applications. In HTSs, weak links of superconductivity are inevitable at high-angle grain boundaries (GBs). Thus, two adjacent grains should be crystallographically aligned within the critical angle (θ_c), for which the intergrain critical current density (J_c) starts to decrease exponentially. The θ_c of several iron-based superconductors (IBSs) is larger than that of cuprates. However, the decreases in both θ_c and intergrain J_c under magnetic fields for IBSs are still substantial, hampering their applications in polycrystalline forms. Here, we report that potassium-doped BaFe₂As₂ (Ba122:K) exhibits superior GB performance to that of previously reported IBSs. A transport J_c of over 0.1 MA/cm² across [001]-tilt GBs with misorientation angles up to θ_GB = 24° was recorded even at 28 K, which is a required level for practical applications. Additionally, even in an applied magnetic field, θ_c was unaltered, and the decay of the intergrain J_c was small. Our results highlight the exceptional potential of Ba122:K for polycrystalline applications and pave the way for next-generation superconducting magnets.