Evidence from EXAFS for Different Ta/Ti Site Occupancy in High Critical Current Density Nb${}_3$Sn Superconductor Wires

Abstract

To meet critical current density, J${}_c$, targets for the Future Circular Collider (FCC), the planned replacement for the Large Hadron Collider (LHC), the high field performance of Nb${}_3$Sn 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${}_3$Sn 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.

arXiv comment14 pages, 6 figures

References in corpus (4)

• Internally Oxidized Nb3Sn Strands with Fine Grain Size and High Critical Current Density
• Examination of the tradeoff between intrinsic and extrinsic properties in the optimization of a modern internal tin Nb3Sn conductor
• Significant enhancement of compositional and superconducting homogeneity in Ti rather than Ta-doped Nb3Sn
• Performance Boost in Industrial Multifilamentary Nb3Sn Wires due to Radiation Induced Pinning Centers

Cited by in corpus (3)

• Beneficial influence of Hf and Zr additions to Nb4at.%Ta on the vortex pinning of Nb${}_3$Sn with and without an O source
• Ta, Ti and Hf effects on Nb${}_3$Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation
• Influence of Nb Alloying on Nb Recrystallization and the Upper Critical Field of Nb3Sn