Investigation of the improvement of superconducting properties of Nb₃Al by introducing non-metallic elements iodine

This research employed the powder-in-tube (PIT) method to facilitate the introduction of the non-metallic element iodine (I) into the preparation of Nb₃Al superconducting wires. After heating in a tube furnace, a rapid heating, quenching, and transformation (RHQT) treatment was conducted. It was observed that as the quantity of iodine introduced increased, the extent of the Nb/Al reaction also rose, indicating that a certain amount of iodine can be introduced to facilitate the Nb/Al reaction, thereby enabling Nb to react more fully with Al in the subsequent process and generating a Nb₃Al superconducting phase that is closer to the stoichiometric ratio. Wires with iodine contents of 1.0 wt%, 1.5 wt%, and 2.0 wt% exhibited a diffusion layer at the Nb/Al interface after heating in a tube furnace at 1000 °C for 30 min. The primary component of the diffusion layer was Nb₂Al. No diffusion layer was observed in the pure sample or in the group with 0.5 wt% I. However, a eutectic phase was present at the edge of Nb and Al. The wires with 1.0 wt% and 1.5 wt% I exhibited higher critical temperatures (T_c) of 18.236 K and 17.421 K, respectively, than the pure sample. Additionally, they demonstrated superior critical current density (J_c) properties compared to the pure sample.