niobiumtin

Niobium tin, chemically Nb3Sn, commonly referred to as niobium-tin, is an intermetallic compound that forms a superconducting A15 phase. It is used primarily in high-field superconducting magnets. In practice Nb3Sn is produced as a diffusion-formed layer around niobium filaments embedded in a copper or bronze matrix; tin diffuses into Nb when the composite is heat-treated at high temperatures (approximately 700–1000°C). Because Nb3Sn is brittle, it cannot be drawn or bent after reaction, so magnet wires are built by shaping the intact Nb–Sn composite and stabilizing it with copper.

Tc is about 18 kelvin; the upper critical field Hc2 at low temperatures can exceed 20 tesla and in optimized materials approaches 25–30 tesla. The material exhibits high critical current densities in high fields, but its performance is sensitive to strain; small mechanical stresses can reduce superconductivity. Doping with titanium or tantalum commonly enhances Hc2 and strain tolerance.

Two main fabrication routes are used: the bronze process, in which Nb filaments are embedded in a tin-bronze matrix and reacted to form Nb3Sn; and the internal tin process, in which tin is delivered to Nb filaments from a Sn-rich core during heat treatment. Both methods aim to maximize Nb3Sn formation while preserving copper stabilization for quench protection.

Applications include high-field magnets for particle accelerators and other scientific instruments; Nb3Sn enables fields beyond those achievable with NbTi. The material continues to be the subject of ongoing research to improve strain tolerance, manufacturability, and performance at higher temperatures.