Tarantini Chiara, Kametani Fumitake, Balachandran Shreyas, Heald Steve M, Wheatley Laura, Grovenor Chris R M, Moody Michael P, Su Yi-Feng, Lee Peter J, Larbalestier David C
National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA.
Department of Mechanical Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, FL, 32310, USA.
Sci Rep. 2021 Sep 8;11(1):17845. doi: 10.1038/s41598-021-97353-w.
In recent years there has been an increasing effort in improving the performance of NbSn for high-field applications, in particular for the fabrication of conductors suitable for the realization of the Future Circular Collider (FCC) at CERN. This challenging task has led to the investigation of new routes to advance the high-field pinning properties, the irreversibility and the upper critical fields (H and H, respectively). The effect of hafnium addition to the standard Nb-4Ta alloy has been recently demonstrated to be particularly promising and, in this paper, we investigate the origins of the observed improvements of the superconducting properties. Electron microscopy, Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS) and Atom Probe Tomography (APT) characterization clearly show that, in presence of oxygen, both fine NbSn grains and HfO nanoparticles form. Although EXAFS is unable to detect significant amounts of Hf in the A15 structure, APT does indeed reveal some residual intragrain metallic Hf. To investigate the layer properties in more detail, we created a microbridge from a thin lamella extracted by Focused Ion Beam (FIB) and measured the transport properties of Ta-Hf-doped NbSn. H(0) is enhanced to 30.8 T by the introduction of Hf, ~ 1 T higher than those of only Ta-doped NbSn, and, even more importantly the position of the pinning force maximum exceeds 6 T, against the typical ~ 4.5-4.7 T of the only Ta-doped material. These results show that the improvements generated by Hf addition can significantly enhance the high-field performance, bringing NbSn closer to the requirements necessary for FCC realization.
近年来，人们越来越致力于提高铌锡（NbSn）在高场应用中的性能，特别是用于制造适合欧洲核子研究组织（CERN）未来环形对撞机（FCC）的导体。这项具有挑战性的任务促使人们研究新的途径来提高高场钉扎性能、不可逆性和上临界场（分别为H和H）。最近已证明，向标准Nb-4Ta合金中添加铪的效果特别有前景，在本文中，我们研究了观察到的超导性能改善的根源。电子显微镜、扩展X射线吸收精细结构光谱（EXAFS）和原子探针断层扫描（APT）表征清楚地表明，在有氧的情况下，会形成细小的NbSn晶粒和HfO纳米颗粒。尽管EXAFS无法检测到A15结构中有大量的铪，但APT确实揭示了一些残余的晶粒内金属铪。为了更详细地研究层状特性，我们用聚焦离子束（FIB）从薄片中制作了一个微桥，并测量了Ta-Hf掺杂的NbSn的输运特性。通过引入铪，H(0)提高到30.8 T，比仅Ta掺杂的NbSn高出约1 T，更重要的是，钉扎力最大值的位置超过6 T，而仅Ta掺杂材料的典型值约为4.5-4.7 T。这些结果表明，添加铪所带来的改善可以显著提高高场性能，使NbSn更接近实现FCC所需的要求。
