@article{6274758b820c4578a50a8afcd117741e,
title = "Grain-boundary structure and segregation in Nb3Sn coatings on Nb for high-performance superconducting radiofrequency cavity applications",
abstract = "We report on atomic-scale analyses of grain boundary (GB) structures and segregation in Nb3Sn coatings on Nb, prepared by the vapor-diffusion process, for superconducting radiofrequency (SRF) cavity applications, utilizing atom-probe tomography, high-resolution scanning transmission electron-microscopy and first-principles calculations. We demonstrate that the chemical composition of Nb3Sn GBs is correlated strongly with the diffusion of Sn and Nb at GBs during the coating process. In a sample coated with a relatively large Sn flux, we observe an interfacial width of Sn segregation at a GB of ∼3 nm, with a maximum concentration of ∼35 at.%. After post-annealing at 1100 °C for 3 h, the Sn segregated at GBs disappears and Nb segregation is observed subsequently at GBs, indicating that Nb diffused into the Nb3Sn GBs from the Nb substrate. It is also demonstrated that the amount of Sn segregation in a Nb3Sn coating can be controlled by: (i) Sn flux; and (ii) the temperatures of the Nb substrates and Sn source, which may affect the overall kinetics including GB diffusion of Sn and Nb. An investigation of the correlation between the chemical compositions of GBs and Nb3Sn SRF cavity performance reveals that the Nb3Sn SRF cavities with the best performance (high-quality factors at high accelerating electric-field gradients) do not exhibit Sn segregation at GBs. Our results suggest that the chemical compositions of GBs in Nb3Sn coatings for SRF cavities can be controlled by GB engineering and can be utilized to optimize fabrication of high-quality Nb3Sn coatings for SRF cavities.",
keywords = "Atom-probe tomography, Grain-boundary segregation, NbSn, Superconducting radio-frequency cavities, Transmission electron microscopy",
author = "Jaeyel Lee and Zugang Mao and Kai He and Sung, {Zu Hawn} and Tiziana Spina and Baik, {Sung Il} and Hall, {Daniel L.} and Matthias Liepe and Seidman, {David N.} and Sam Posen",
note = "Funding Information: We are grateful to Drs. Amir R. Farkoosh, Xiaobing Hu, Dieter Isheim, Shipeng Shu, Xingchen Xu, Xuefeng Zhou and Mr. Qingqiang Ren for valuable discussions, and Mr. Brad Tennis for assistance in processing Nb3Sn coatings. We also thank Profs. Thomas Arias, David A. Muller, and James P. Sethna for their valuable suggestions. This research is supported by the United States Department of Energy, Offices of High Energy. Fermilab is operated by the Fermi Research Alliance LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. This work made use of the EPIC, Keck-II, and/or SPID facilities of Northwestern University's NUANCE Center, which received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Cornell's Nb3Sn coating program is supported by United States Department of Energy grant DE-SC0008431. Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with grants from the NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, N00014-0910781, N00014-1712870) programs. NUCAPT received support from the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the SHyNE Resource (NSF ECCS-1542205), and the Initiative for Sustainability and Energy (ISEN) at Northwestern University. Funding Information: We are grateful to Drs. Amir R. Farkoosh, Xiaobing Hu, Dieter Isheim, Shipeng Shu, Xingchen Xu, Xuefeng Zhou and Mr. Qingqiang Ren for valuable discussions, and Mr. Brad Tennis for assistance in processing Nb 3 Sn coatings. We also thank Profs. Thomas Arias, David A. Muller, and James P. Sethna for their valuable suggestions. This research is supported by the United States Department of Energy, Offices of High Energy. Fermilab is operated by the Fermi Research Alliance LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. This work made use of the EPIC, Keck-II, and/or SPID facilities of Northwestern University's NUANCE Center, which received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource ( NSF ECCS-1542205 ); the MRSEC program ( NSF DMR-1121262 ) at the Materials Research Center ; the International Institute for Nanotechnology (IIN); the Keck Foundation ; and the State of Illinois , through the IIN. Cornell's Nb 3 Sn coating program is supported by United States Department of Energy grant DE-SC0008431 . Atom-probe tomography was performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with grants from the NSF-MRI ( DMR-0420532 ) and ONR-DURIP ( N00014-0400798 , N00014-0610539 , N00014-0910781 , N00014-1712870 ) programs. NUCAPT received support from the MRSEC program ( NSF DMR-1720139 ) at the Materials Research Center , the SHyNE Resource ( NSF ECCS-1542205 ), and the Initiative for Sustainability and Energy (ISEN) at Northwestern University. Publisher Copyright: {\textcopyright} 2020 Acta Materialia Inc.",
year = "2020",
month = apr,
day = "15",
doi = "10.1016/j.actamat.2020.01.055",
language = "English (US)",
volume = "188",
pages = "155--165",
journal = "Acta Materialia",
issn = "1359-6454",
publisher = "Elsevier Limited",
}