Recent Progress of Iron-Based Superconducting Round Wires

Recent progress of round wires using iron-based superconductors is reviewed. Both transport and magnetic Jc have been enhanced by several techniques such as purification of polycrystalline powders, high-pressure sintering (HIP), and control of drawing and sintering conditions. The present record of transport Jc of round wires is realized when the wire with 122-type compounds is processed at 175 MPa with a value at 4.2 K under 100 kOe being 38 kA/cm2 using (Ba,K)Fe2As2. We also discuss HIP round wires of (Sr,K)Fe2As2 and recently fabricated CaKFe4As4. Details of the optimization of round wires to achieve large Jc values are described.