The effect of strain on the martensitic phase transition in superconducting Nb3Sn

The connection between the cubic-to-tetragonal martensitic phase transformation and the phenomenon of superconductivity in A15 compounds is being investigated. The degradation of the critical parameters, such as Tc, Hc2, and Jc, with mechanical straining is of particular interest. Since martensitic transitions are also known to be strain sensitive, perhaps the structural change is directly responsible for the reduction in superconducting properties. We performed low-temperature x-ray diffraction experiments on Nb3Sn ribbons (with the bronze layers etched off) mounted on copper and indium sample stages. The cryostat we used is unique in that it has a vacuum mechanical insert which allows the superconductor to be placed under both compressive and tensile strains while at low temperatures. Preliminary results indicate that the martensitic phase transition temperature, Tm, increases with compressive strains. Other effects of strain on tetragonal phase production are also discussed.