Fabrication of Large and High-Performance FeSe Bulk Superconductors by a Simple Liquid–Solid Diffusion Method

FeSe polycrystalline superconductors with dimensions over 10 × 10 × 3 mm³ were fabricated by diffusing liquid Se into an iron tablet at 650 °C. Scanning electron microscopy and X-ray diffraction analyses were performed on the FeSe samples, and they showed that the main phase throughout the bulk is tetragonal β-FeSe and the grains are well crystallized and connected. The critical transition temperature (onset) was determined to be 12 K, with a transition width of 3 K, by a resistivity measurement. The upper critical fields H_c2(0) was estimated to be 40 T, and the intragranular critical current density estimated from the Bean model is about 1.5 × 10⁵ A/cm² at 4 Kin self-field. These results suggest that liquid-solid diffusion is a promising technique for fabricating large and high-quality FeSe bulk superconductors.