Niobium-tin

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Niobium-tin (Nb₃Sn) is a metallic chemical compound of niobium (Nb) and tin (Sn), used industrially as a type II superconductor. It is more expensive than niobium-titanium (NbTi), but can withstand magnetic field intensity values up to 30 T, whereas NbTi can withstand only up to roughly 10 T. Mechanically, Nb₃Sn is extremely brittle and thus can not be easily drawn into a wire, which is necessary for winding superconducting magnets. To overcome this, wire manufacturers typically draw down composite wires containing ductile precursors. The "internal tin" process include separate alloys of Nb, Cu and Sn. The "bronze" process contains Nb in a copper-tin bronze matrix. With both processes the strand is typically drawn to final size and coiled into a solenoid or cable before heat treatment. It is only during the heat treatment that the Sn reacts with the Nb to form the brittle, superconducting niobium-tin compound.

Its critical temperature is 18.3 kelvins (K). It is usually used at 4.2 K, the boiling point of liquid helium.

The central solenoid and toroidal field superconducting magnets used in the ITER fusion reactor use niobium-tin as a superconductor. The high field section of modern NMR magents are composed of niobium-tin wire.

Nb₃Sn was discovered to be a superconductor in 1954.