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 BaFe 2 As 2 (Ba122:K) exhibits superior GB performance to that of previously reported IBSs. A transport J c of over 0.1 MA/cm 2 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. We have fabricated artificial grain boundaries in K-doped BaFe 2 As 2 (Ba122:K), one of the Fe-based superconductors. The crystalline orientation map, acquired through the scanning precession electron diffraction measurements, revealed that spontaneous connectivity modification occurred at the grain boundary, which may mitigate weak-link behavior. Specifically, a self-field critical current density J c of over 0.1 MA/cm 2 across the grain boundary with misorientation angles up to 24° was recorded even at 28 K. This performance surpasses the grain boundary properties of hitherto reported Fe-based superconductors. Our results highlight the exceptional potential of Ba122:K for polycrystalline applications and pave the way for next-generation superconducting magnets.