Recent breakthrough development in iron-based superconducting wires for practical applications

Abstract

Iron-based superconductors (IBSs), discovered in 2008, formed the second high-Tc superconductor family after cuprate superconductors, and over the past decade have been the subject of extensive research into their physical nature and application potential. With their attractions of very high upper critical fields and small electromagnetic anisotropy, tremendous advances have been made in wire research and development (R&D) to explore the potential of IBSs for high-field applications. In recent years, rapid progress was made on the critical current density (Jc) of the 122-type IBS wires based on a powder-in-tube technique. Encouraging breakthroughs were made, including a high transport Jc exceeding the practical level of 105 A cm−2 (at 4.2 K, 10 T) and the first 100 meter-class wire. This review covers the state-of-the-art techniques and their mechanism in realizing high transport Jc with respect to the grain connectivity, grain texture and flux pinning for IBS wires and tapes, as well as the temperature and field angle dependence of critical currents. The mechanical properties, AC losses and magneto-thermal stability of IBS wires are investigated, and further improvements in IBS conductors for large-scale applications are proposed. In addition to long wire fabrication, this review also highlights some remarkable advances relevant to practical applications, including scalable process optimization, copper sheaths, multifilamentary fabrication, and superconducting joints. Finally, a summary and outlook for R&D for IBS wires are presented.

High Jc and low anisotropy of hydrogen doped NdFeAsO superconducting thin film

“…The Fe-based superconductors (FBS), the second class of high-temperature superconductors beside the cuprates, are considered as possible candidates for high-field magnet applications 1 – 5 . Among them, Ln FeAs(O,F) ( Ln : Nd and Sm) has the highest depairing current density J d of ~ 170 MA/cm 2 at zero kelvin 6 .…”

Superconducting materials: Challenges and opportunities for large-scale applications

“…In the past years, mechanical deformation processes such as flat rolling, isostatic pressing, and uniaxial pressing have significantly improved the J c of 122-type IBS in USA, Europe, China, Japan, and Australia ( Weiss et al, 2012 ; Malagoli et al, 2015 ; Zhang et al, 2014 ; Gao et al, 2017 ; Shabbir et al, 2017 ). High transport J c above the practical level of 10 5 A/cm 2 (4.2 K, 10 T) has been achieved by hot or cold uniaxial press combined with flat rolling process for PIT wires and tapes ( Hosono et al, 2018 ; Yao and Ma, 2019 ). A synergetic microstructural tailoring for mass density, grain alignment and micro-cracks is the key to realize such high J c performance.…”

“…Last year, a practical level critical current density up to 1.1 × 10 5 A cm −2 at 4.2 K and 10 T was achieved in Cu/Ag sheathed Ba-122 tapes by combing flat rolling to induce grain texture and a subsequent HIP densification, which is a scalable and cost-effective manufacturing route ( Liu et al, 2021 ).

Figure 7 State-of-the-art critical current density J c of 122-IBS based on PIT technique showing much weaker field dependence up to 33 T compared with that of Nb-Ti and Nb 3 Sn LTS conductors Data source for IBS short samples: Ba-122 tapes ( J c at 10-13 T, 24-27 T and 25-33 T were measured in a 14 T superconducting magnet, a 28 T hybrid magnet and a 35 T water-cooled magnet, respectively) ( Yao and Ma, 2019 ; Huang et al, 2018 ); Ba-122 wires ( Pyon et al, 2020 ). Data for LTS conductors were collected from nationalmaglab.org ( Lee, 2018 ).

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Microstructure and Flux Pinning of Reacted-and-Pressed, Polycrystalline Ba0.6K0.4Fe2As2 Powders

“…Regarding possible applications, the 122 compounds can operate at higher magnetic fields than MgB 2 [2], are less prone to flux jumps, are robust to impurity doping [3], and the misalignment of the grains can be higher than in cuprates when producing wires or bulks. These advantages were already manifested in several efforts to produce 122-based wires/tapes (see, e.g., the recent review of Yao et al [4]), and trapped fields above 1 T were already recorded in bulk, HIP (hot isostatic pressed)-processed 122 samples [5]. On the other hand, the 122 material demonstrates several unique properties, e.g., it undergoes an isostructural transition under pressure [6,7,8,9], from which important information on the nature of superconductivity can be obtained.…”

“…This was discussed in detail in several publications [11,12,13,14]. The recent advances in jc of tapes [4] and bulk materials [5,15,16] are, therefore, due to these improved sample preparation routes.…”