Based on molecular dynamics (MD) simulations of Nb3Sn crystals under high pressure, a physics-based trans -scale model of the superconducting transition of high-pressure Nb3Sn is proposed. This model investigates the electromechanical coupling effect of Nb3Sn and discusses the effect of grain boundary deformation on electro-mechanical coupling through simulations. The simulated results demonstrate that the strain-induced electronic structure evolution and accompanying variations in the density of states (DOS) at the Fermi surface control the superconducting transition of single-crystal Nb3Sn. This effect is amplified by the stress concentrations at the grain boundary intersections, leading to the obviously different electromechanical responses of high-pressure single-crystal and polycrystal Nb3Sn. It was further found that the electromechanical coupling effect in Nb3Sn was scale coupled, including a strain-regulated electronic structure, grain boundary contours of strained Nb3Sn at the atomic scale, local atom stress distribution, and intrinsic connections between the strain-modulated super-conducting and normal-state transport properties (at the macroscale level). The linkage between the micro-meso-macro-scales was qualitatively reproduced by the proposed model, where the three principal strain components and their differences represent the response-controlling parameters. The grain boundary zone was critical to further determine the reversible-irreversible transition of the electromechanical coupling effects in Nb3Sn. The proposed analytical and simulation models provided important theoretical guidance for understanding the empirical relation obtained experimentally. Additionally, they presented a method for the parameterization of electromechanical coupling in Nb3Sn.

Molecular-dynamics simulation; Nb3Sn; grain boundary deformation; superconducting transition; critical temperature degradation

Taiyuan University of Technology