Analysis of the strain dependence of the superconducting critical properties of single-crystal and polycrystalline Nb3Sn

Abstract

The aim of this article is to present a three-dimensional (3D) simulation based on Voronoi tessellation, used to assess the strain dependence of the superconducting critical properties of inhomogeneous polycrystalline Nb3Sn at the microstructural level. To support this objective, we first present a polycrystalline model with equiaxed grains used to analyze the relationship between the polycrystalline structure and the strain response. We analyze the Young’s moduli of Nb3Sn at different temperatures with random and preferential polycrystalline orientations, and the relation between the Young’s modulus of polycrystalline Nb3Sn and spontaneous tetragonal transformation is discussed. The results indicate that the elastic properties (Young’s modulus, stress/strain field) of polycrystalline Nb3Sn are mainly associated with ambient temperature and phase transition and are affected by the grain orientation. Meanwhile, an estimation-based model for the superconducting critical properties of single-crystal Nb3Sn is proposed. This model is based on changes in the electron density of states and phonon frequency induced by strain. The results calculated by the estimation-based model are consistent with the experimental data and the values calculated according to first principles. The change in the strain-induced superconducting properties of polycrystalline Nb3Sn is analyzed by combining the numerically simulated strain field of the polycrystal with the estimation-based model of single-crystal Nb3Sn. Compared to ideal single-crystal Nb3Sn, the superconducting critical temperature of the polycrystalline Nb3Sn superconductor has a higher strain sensitivity, which is related to the non-uniformity of the strain field of the polycrystal.