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Title: Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density Nb 3Sn Superconductor Wires

To meet critical current density, Jc, targets for the Future Circular Collider (FCC), the planned replacement for the Large Hadron Collider (LHC), the high field performance of Nb 3Sn must be improved, but champion J c values have remained static for the last 10 years. Making the A15 phase stoichiometric and enhancing the upper critical field H c2 by Ti or Ta dopants are the standard strategies for enhancing high field performance but detailed recent studies show that even the best modern wires have broad composition ranges. To assess whether further improvement might be possible, we employed EXAFS to determine the lattice site location of dopants in modern high-performance Nb 3Sn strands with J c values amongst the best so far achieved. Although Ti and Ta primarily occupy the Nb sites in the A15 structure, we also find significant Ta occupancy on the Sn site. These findings indicate that the best performing Ti-doped stand is strongly sub-stoichiometric in Sn and that antisite disorder likely explains its high average H c2 behavior. These new results suggest an important role for dopant and antisite disorder in minimizing superconducting property distributions and maximizing high field J c properties.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [2] ; ORCiD logo [2] ; ORCiD logo [3] ;  [4] ; ORCiD logo [2]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  2. Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab. (MagLab)
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  4. Brookhaven National Lab. (BNL), Upton, NY (United States). Magnet Division
Publication Date:
Grant/Contract Number:
SC0012083; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 8; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Florida State Univ., Tallahassee, FL (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; 43 PARTICLE ACCELERATORS; Nb3Sn; superconductors; RRP; microstructure; EXAFS; doping; lattice sites
OSTI Identifier:
1429849
Alternate Identifier(s):
OSTI ID: 1432371