Reaction-based mechanism for Nb3Sn nucleation: Role of oxygen

Intermetallic Nb3Sn alloys have long been believed to form through Sn diffusion into Nb via grain boundaries. However, our observations of significant oxygen content in Nb3Sn prompted investigation of alternative formation mechanisms. Through experiments involving different oxide interfaces (clean HF-treated, native oxidized, and anodized), we demonstrate a fundamentally new reaction-based mechanism for Nb3Sn nucleation, which deviates from the previously known diffusion-based mechanism. Our findings highlight the critical involvement of a SnOx intermediate phase that further reduces to metallic Sn, leading to alloy nucleation. This new mechanism identifies the principles for growth optimization and new synthesis of high-quality Nb3Sn superconductors.