Elastic constants of polycrystalline Nb3Sn between 4.2 and 300 K

The three elastic constants of polycrystalline Nb₃Sn have been measured between 4.2 and 300 K using an ultrasonic pulse propagation technique in composite ribbons of Nb₃Sn/Nb. Both the shear (G) and Young's (E) moduli are found to soften dramatically on cooling to the superconducting temperature, with no abrupt change or hardening near or below the martensitic phase transformation (43 K). Poisson's ratio is also found to change considerably on cooling, increasing from 0.22 at 300 K to 0.46 at 30 K. These results confirm and complement static and low frequency measurements on similar ribbons but disagree with previous values obtained ultrasonically on bulk samples which exhibited very little softening. Comparison of the present results with polycrystalline averages of single crystal data assuming different textures indicate that deviations are probably associated with material differences and not texture.