Xinhua Li,Qingshuang Ma,Ji Dong,Tansir Ahamad,Zongqing Ma
The Nb 3 (Al 1− x Sn x ) superconductor with enhanced critical current density ( J c ) is prepared by the process of mechanical alloying (MA) and subsequent low-temperature sintering and the enhancement mechanism of J c in Nb 3 (Al 1− x Sn x ) is discussed. The analysis of the flux pinning force implies that there is an additional pinning mechanism apart from grain boundary pinning in Nb 3 (Al 1− x Sn x ). The existence of dispersed Nb 2 Al nanoparticles (<30 nm) in Nb 3 (Al 1− x Sn x ) is confirmed by microstructure observation. These nanosized Nb 2 Al particles can serve as flux pinning centers, which leads to the increase of the flux pinning force as well as the enhancement of Nb 3 (Al 1− x Sn x )'s J c performance.
This research employed the powder-in-tube (PIT) method to facilitate the introduction of the non-metallic element iodine (I) into the preparation of Nb 3 Al superconducting wires. After heating in a tube furnace, a rapid heating, quenching, and transformation (RHQT) treatment was conducted. It was observed that as the quantity of iodine introduced increased, the extent of the Nb/Al reaction also rose, indicating that a certain amount of iodine can be introduced to facilitate the Nb/Al reaction, thereby enabling Nb to react more fully with Al in the subsequent process and generating a Nb 3 Al superconducting phase that is closer to the stoichiometric ratio. Wires with iodine contents of 1.0 wt%, 1.5 wt%, and 2.0 wt% exhibited a diffusion layer at the Nb/Al interface after heating in a tube furnace at 1000 °C for 30 min. The primary component of the diffusion layer was Nb 2 Al. No diffusion layer was observed in the pure sample or in the group with 0.5 wt% I. However, a eutectic phase was present at the edge of Nb and Al. The wires with 1.0 wt% and 1.5 wt% I exhibited higher critical temperatures ( T c ) of 18.236 K and 17.421 K, respectively, than the pure sample. Additionally, they demonstrated superior critical current density ( J c ) properties compared to the pure sample.
Yaqi He,Xinhua Li,Zhu Qian,ZuPeng Yan,Guizhen Shi,Xia Sun,Zongqing Ma
In this paper, we innovatively introduced Sn and B into the Nb-Al system at the same time and successfully prepared high-performance Nb 3 Al bulks through mechanical alloying and subsequent low-temperature sintering processes. The influence of different doping amounts of B in the Sn-B co-doping on the superconducting properties of Nb 3 Al superconductors was also investigated. It was found that Sn-B co-doping greatly improves the superconducting properties of Nb 3 Al, especially the J c properties, compared with the undoped sample. The optimal doping amount of Sn-B co-doping is finally determined to be 4 at% Sn-2.6 at% B. At this time, the superconducting transition temperature of Nb 3 Al is up to 16.2 K, and the critical current density reaches up to 1.3 × 10 5 A⋅cm −2 (4.2 K, 5 T), which is almost twice higher than that of Sn-doped Nb 3 Al, and one order of magnitude higher than that of general undoped Nb 3 Al. Combined with the phase composition analysis and microstructure observation, we find that with the co-doping of Sn and B, the grain size of Nb 3 Al is refined, and the diffusely distributed Nb 2 Al nanoparticles are introduced, which greatly enhance the magnetic flux pinning effect of Nb 3 Al. Secondly, the intergranular connectivity of Nb 3 Al is significantly improved. The Sn-B co-doped Nb 3 Al superconductors combine the advantages of Sn doping to enhance flux pinning and B doping to improve intergranular connectivity, which synergistically promotes the dramatic improvement of Nb 3 Al superconductivity Nb 3 Al.
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