Strain Dependence of the Critical Temperature Tc of Polycrystalline Nb3Sn Superconductors

The polycrystalline nature of Nb₃Sn introduces crystal orientation as a possible variable in the strain dependence of the critical properties. It is shown that a dependence of strain sensitivity on crystal orientation implies a dependence on strain of the distribution of T_c, with implications for the functional dependence of strain sensitivity on the strain tensor. The distribution of T_c is found to have an influence on the characteristics of the resistive transition of T_c . Calculations of the resistive transition are done under alternative assumptions for the crystal orientation dependence of strain sensitivity. Available data on the strain dependence of the transition of T_c are contradictory and inconclusive. If strain sensitivity were found to be independent of grain orientation, that would imply a strain dependence on the entire deviatoric strain tensor, through the scalar invariants, including the tetragonal and shear parts. This would be a surprising conclusion given the emphasis on tetragonal strain in Nb₃Sn .