Thermodynamic route of Nb3Sn nucleation: Role of oxygen.

Intermetallic Nb₃Sn alloys have long been believed to form through Sn diffusion into Nb. However, our observations of significant oxygen content in Nb₃Sn prompted an investigation of alternative formation mechanisms. Through experiments involving different oxide interfaces (clean HF-treated, native oxidized, and anodized), we demonstrate a thermodynamic route that fundamentally challenges the conventional Sn diffusion mechanism for Nb₃Sn nucleation. Our results highlight the critical involvement of a SnO_x intermediate phase. This new nucleation mechanism identifies the principles for growth optimization and new synthesis of high-quality Nb₃Sn superconductors. [ABSTRACT FROM AUTHOR]