Nb3Sn

Nb3Sn, or niobium-tin, is an intermetallic compound that becomes superconducting below about 18 kelvin. It crystallizes in the A15 crystal structure and is a Type II superconductor with a high upper critical field, enabling operation in magnetic fields in the tens of teslas. The material is formed by reacting niobium with tin within a composite wire through a diffusion heat treatment. Tin diffuses into niobium at high temperatures (approximately 650–750 °C) to produce Nb3Sn, which is responsible for the superconducting properties.

In practice, Nb3Sn is used in a brittle form, so wires are manufactured with a ductile matrix, such as copper or bronze, to provide mechanical support and electrical stabilization. Two common fabrication routes are the Bronze Route, where Nb filaments are embedded in a copper-tin bronze matrix and tin diffuses into Nb to form Nb3Sn, and the Internal Tin Route, in which tin is supplied from an internal source during heat treatment. Nb3Sn wires exhibit high critical current densities in strong magnetic fields, with upper critical fields around 20–25 T at 4.2 K and potentially higher as temperature decreases. However, the brittleness of Nb3Sn and its sensitivity to strain require careful coil design, handling, and heat-treatment schedules.

Applications include high-field magnets for fusion devices (such as ITER), high-energy physics accelerators, and certain medical imaging systems that demand fields beyond the capabilities of Nb-Ti conductors. Ongoing research aims to improve critical current density, strain tolerance, and manufacturability, as well as to develop improved processing methods and alternative materials.