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Title: Analysis of Nb{sub 3}Sn surface layers for superconducting radio frequency cavity applications

We present an analysis of Nb{sub 3}Sn surface layers grown on a bulk Niobium (Nb) coupon prepared at the same time and by the same vapor diffusion process used to make Nb{sub 3}Sn coatings on 1.3 GHz Nb cavities. Tunneling spectroscopy reveals a well-developed, homogeneous superconducting density of states at the surface with a gap value distribution centered around 2.7 ± 0.4 meV and superconducting critical temperatures (T{sub c}) up to 16.3 K. Scanning transmission electron microscopy performed on cross sections of the sample's surface region shows an ∼2 μm thick Nb{sub 3}Sn surface layer. The elemental composition map exhibits a Nb:Sn ratio of 3:1 and reveals the presence of buried sub-stoichiometric regions that have a ratio of 5:1. Synchrotron x-ray diffraction experiments indicate a polycrystalline Nb{sub 3}Sn film and confirm the presence of Nb rich regions that occupy about a third of the coating volume. These low T{sub c} regions could play an important role in the dissipation mechanisms occurring during RF tests of Nb{sub 3}Sn-coated Nb cavities and open the way for further improving a very promising alternative to pure Nb cavities for particle accelerators.
Authors:
 [1] ;  [2] ;  [2] ; ;  [3] ; ;  [1] ;  [2] ;  [4] ;  [5] ;  [3] ;  [2] ;  [1] ;  [6]
  1. Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
  2. (United States)
  3. Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York 14853 (United States)
  4. Nanoscience and Technology Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
  5. X-ray Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
  6. Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616 (United States)
Publication Date:
OSTI Identifier:
22412709
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 8; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COATINGS; CRITICAL TEMPERATURE; CROSS SECTIONS; DENSITY OF STATES; DIFFUSION; FILMS; GHZ RANGE; LAYERS; NIOBIUM BASE ALLOYS; POLYCRYSTALS; RADIOWAVE RADIATION; SUPERCOMPUTERS; SURFACES; TIN ALLOYS; TRANSMISSION ELECTRON MICROSCOPY; TUNNEL EFFECT; X-RAY DIFFRACTION