Investigation of &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$J_{c}$&lt;/tex-math&gt;&lt;/inline-formula&gt;-Suppressing Factors in Flat-Rolled &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{Sr}_{0.6}\hbox{K}_{0.4}\hbox{Fe}_{2}\hbox{As}_{2}/\hbox{Fe}$&lt;/tex-math&gt;&lt;/inline-formula&gt; Tapes Via Microstructure Analysis

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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.

Section: Weak-link Effects and Grain Texturesupporting

confidence: 54%

mentioning

confidence: 60%

Section: Microstructural Defects and Grain Connectivitymentioning

confidence: 99%

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

Yao¹,

Ma²

2019

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“…However, the distribution of Sn is very interesting. Zhang et al believe that the added Sn works to assist the sintering [37]. Considering the relatively lower sintering temperature, adding Sn to assist the sintering was adopted.…”

Section: Resultsmentioning

confidence: 99%

High critical current density in Cu/Ag composited sheathed Ba_0.6K_0.4Fe₂As₂ tapes prepared via hot isostatic pressing

Liu

Cheng

Yao

et al. 2019

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Iron-based superconductors (IBSs) with ultrahigh upper critical fields and low anisotropies have attracted significant attention in terms of the novel mechanism of superconductivity and high-field applications. A major concern for practical research is the fabrication of long wires with enhanced critical current density and low cost. In this paper, Cu/Ag composited sheathed Ba0.6K0.4Fe2As2 (Ba122) tapes were fabricated through a hot isostatic pressing method, which is feasible for long-wire manufacturing. The Cu/Ag composite sheath can lower the tape cost by reducing the use of expensive Ag. A high-transport critical current density (Jc) up to 5.8 × 104 A cm−2 under 10 T at 4.2 K was achieved in our tapes. Evidence has shown that these tapes have pure Ba122 phase, homogeneous element distribution, orientated grains and good grain connectivity. Our work shows that low-cost Cu/Ag-sheathed IBS tapes have great promise for practical applications in the future.

“…A high magnification HAADF-STEM image (b) and a high resolution TEM image (c) reveal that there are stacking faults of Fe-As layers on (001) planes in region 'A', and that region 'B' is an amorphous layer with a width of 2 nm. Amorphous layers on grain boundaries are also reported to exist in the Sr-122 polycrystalline bulk material [33,34]. T cM values are defined as the temperature at which the decrease magnetization |4πM/H| becomes 90% of the difference between those at the superconducting and normal states, i.e., the difference between |4πM/H| at 30 K and 10 K, and f shield values are defined by |4πM/H|×100% at 10 K. T cM increased with the heating temperature, and T cM higher than 23 K was observed for the samples heated above 600 °C.…”

Section: Inter-and Intra-granular Structuresmentioning

confidence: 94%

The formation of defects and their influence on inter- and intra-granular current in sintered polycrystalline 122 phase Fe-based superconductors

Shimada¹,

Yamamoto²,

Hayashi³

et al. 2019

The evolution of intra-and inter-granular structures in Co-doped BaFe 2 As 2 (Ba-122) has been studied to address key issues associated with limited inter-granular current transport in randomly oriented polycrystalline Fe-based superconducting materials. We found that the following phenomena occur with an increase in reaction temperature: (i) significant grain growth; (ii) formation and evolution of two types of cracks; (iii) enhancement in the intra-granular current loop; (iv) reduction of magnetic shielding volume; and (v) decrease of the inter-granular transport current. A strong correlation between the inverse grain size and the inter-granular current density was observed. These results indicate that the key microstructural feature to achieve high transport current is a small grain size with no inter-granular cracks, and that low temperature synthesis is an effective path to this end. Based on the observed stacking faults and inter-granular amorphous layers, we propose a model for the formation of the two types of cracks in a polycrystalline Ba-122 phase, i.e. intra-and inter-granular cracks.