Journal
SUPERCONDUCTOR SCIENCE & TECHNOLOGY
Volume 32, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1361-6668/aaf268
Keywords
Nb3Sn; defects; orientation relationship; superconducting radiofrequency cavity; transmission electron microscopy
Categories
Funding
- United States Department of Energy, Offices of High Energy
- United States Department of Energy [DE-SC0008431, DE-AC02-07CH11359]
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource [NSF ECCS-1542205]
- MRSEC program at the Materials Research Center [NSF DMR-1720139, NSF DMR-1121262]
- International Institute for Nanotechnology (IIN)
- Keck Foundation
- State of Illinois, through the IIN
- Initiative for Sustainability and Energy (ISEN) at Northwestern University
- SHyNE Resource [NSF ECCS-1542205]
- U.S. Department of Energy (DOE) [DE-SC0008431] Funding Source: U.S. Department of Energy (DOE)
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We report on atomic-scale analyses of the microstructure of an Nb3Sn coating on Nb, prepared by a vapor diffusion process for superconducting radiofrequency (SRF) cavity applications using transmission electron microscopy, electron backscatter diffraction and first-principles calculations. Epitaxial growth of Nb3Sn on a Nb substrate is found and four types of orientation relationships (ORs) at the Nb3Sn/Nb interface are identified by electron diffraction or high-resolution scanning transmission electron microscopy (HR-STEM) analyses. Thin Nb3Sn grains are observed in regions with a low Sn flux and they have a specific OR: Nb3Sn (1 (2) over bar0)//Nb ((1) over bar 11) and Nb3Sn (002)//Nb (0 (1) over bar1). The Nb3Sn/Nb interface of thin grains has a large lattice mismatch, 12.3%, between Nb (0 (1) over bar1) and Nb3Sn (002) and a high density of misfit dislocations as observed by HR-STEM. Based on our microstructural analyses of the thin grains, we conclude that the thin regions are probably a result of a slow interfacial migration with this particular OR. The Sn-deficient regions are seen to form initially at the Nb3Sn/Nb interface and remain in the grains due to the slow diffusion of Sn in bulk Nb3Sn. The formation of Sn-deficient regions and the effects of interfacial energies on the formation of Sn-deficient regions at different interfaces are estimated by first-principles calculations. The finding of ORs at the Nb3Sn/Nb interface provides important information about the formation of imperfections in Nb3Sn coatings, such as large thin-regions and Sn-deficient regions, which are critical to the performance of Nb3Sn SRF cavities for accelerators.
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