Enhancement of critical current density in (Ba,Na)Fe2As2 round wires using high-pressure sintering

We fabricated (Ba,Na)Fe₂As₂ superconducting wires using the powder-in-tube method and hot isostatic pressing. By improving powder synthesis processes compared with previous studies, highly pure raw materials for the wire fabrication were obtained. The largest transport critical current density (J_c) reached 40 kA cm^-2 at T = 4.2 K under a magnetic field of 100 kOe. This value exceeds not only the value of transport J_c of the previous (Ba,Na)Fe₂As₂ wire but also those of all iron-based superconducting round wires. Improvements of polycrystalline powder synthesis play a key role for the enhancement of J_c. Furthermore, it was clarified that higher densification by high-pressure sintering and the texturing of grains in the core of the wire due to drawing also increased J_c effectively. Advantages of (Ba,Na)Fe₂As₂ wires compared with (Ba,K)Fe₂As₂ wires are also discussed.