Effect of Compressive Deformation on the Martensitic Transformation Temperature In Superconducting Nb3sn

Abstract

The superconducting Nb3Sn, designed for high-field magnet fabrication, offers significant potential for applications ranging from the international thermonuclear experimental reactor (ITER) to a demonstration power plant (DEMO). Mechanical and electromechanical properties of Nb3Sn are essential for designing future high-field magnets. High-pressure experiments on mixed-phase Nb3Sn reveal that the maximum resistivity change occurs near 40 K under uniaxial compressive strain, suggesting a strong influence of the cubic-tetragonal martensitic transformation on low-temperature resistivity. The origin of anomalous low-temperature resistivity changes in strained Nb3Sn remains debated. By analyzing phonon and electronic properties of uniaxially strained Nb3Sn during phase transitions, we developed a semi-analytical trans-scale electromechanical model to characterize its low-temperature resistivity. Resistivity variations of mixed-phase Nb3Sn under uniaxial compressive strain predicted by this model match experimental results, emphasizing the effect of compression deformation on the tetragonal-to-cubic phase transition of superconducting Nb3Sn. Our first-principles calculations show that superconducting Nb3Sn has a high density of states (DOS) near the Fermi energy level (EF) in the cubic structure, attributed to compact Nb chains. This DOS significantly affects electromechanical coupling behavior. Distortions in Nb chains during phase transitions and strain states alter electronic density of states at Fermi surface (N(EF)). Sublattice distortions are critical for understanding how phase transitions influence low-temperature resistivity in Nb3Sn. The analytical and simulation models proposed deepen the understanding of electromechanical behavior in superconducting Nb3Sn, providing critical insights for future DEMO magnet fabrication and performance evaluation.

Keywords: A15 Nb3Sn, Martensitic transformation temperature, Compression deformation, Electromechanical coupling, Low-temperature resistivity