52 巻 (2017) 6 号 p. 415-421
In a history of superconductors 1911-2017, Fe-based superconductor ReFePnO1-xFx (Re: rare earth, Pn: Pnictogen) exhibits relative high superconducting transition temperatures (Tc) ≤ 58 K under ambient pressure. Electron doping by substitution of O2- with F- was required for appearance of a superconducting phase with high Tc. The Tc and upper critical field of ReFePnO1-xFx are very attractive for applications as superconducting wires and tapes under high magnetic fields, although demonstration of practical superconducting wires is a tough challenge due to the difficulty in controlling the F contents during a processing for ex-situ powder in tube method. In 2017, Zhang et al. reported that iron-based superconducting tapes with Cu sheath showed superconducting electrical current (Jc) ~ 18 kAcm−2. It is noteworthy that the tapes are sintered at 300°C.