Solid-state potassium fluoride doping strategy for stable fabrication of iron-based superconductors

The utilization of reactive alkali metals in solid-state synthesis poses significant challenges for large-scale production of iron-based superconductors (IBS). Particularly for Ba 1 − x K x Fe 2 As 2 (BaK122), an IBS with proven high-field applicability, the extreme air sensitivity and explosive hydrolysis of potassium (K) metal hinder its practical manufacturing. In this work, an innovative approach substitutes elemental K with air-stable potassium fluoride (KF) to achieve the first successful synthesis of BaK122 superconductors, eliminating hazardous handling while maintaining stoichiometric control. The transition temperature of the BaK122 synthesized with KF (KF-based) reaches 38.5 K, consistent with those prepared using elemental K. IBS tapes were manufactured using the KF-based precursors via the powder-in-tube (PIT) method. The effects of thermal treatments at varied temperatures were thoroughly examined, with optimized tapes exhibiting high critical current density ( J c ). Comprehensive microstructural analysis uncovers grain structure and compositional homogeneity, offering essential guidance for additional J c enhancement. KF is confirmed as a reliable potassium source that avoids the intrinsic instability of metallic K, facilitating industrial-scale fabrication of BaK122 superconductors. This materials innovation also establishes a novel strategy for the safe fabrication of potassium-containing inorganic nonmetallic materials. • KF compound can serve as a stable potassium source for the preparation of BaK122 superconductors. • The transition temperature of the BaK122 synthesized with KF reaches 38.5 K, consistent with those prepared using elemental K. • At 4.2 K, the transport critical current density of KF-based tapes achieved 6.3 × 10 4 A/cm 2 at 10 T and 3.7 × 10 4 A/cm 2 at 25 T, respectively.