Strain sensitivity and superconducting properties of Nb3Sn from first principles calculations

• Published in: Journal of physics. Condensed matter Vol. 25; no. 13; pp. 135702 - 135708
• Main Authors: De Marzi, G, Morici, L, Muzzi, L, della Corte, A, Buongiorno Nardelli, M
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 03.04.2013; Institute of Physics
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electrical engineering. Electrical power engineering; Exact sciences and technology; Granular, melt-textured, amorphous and composite superconductors; Inhomogeneous superconductors and superconducting systems; Materials; Physics; Superconductivity; Strain rate sensitivity; Band structure; Superconducting transitions; Brillouin zones; A-15 compounds; Electron-phonon interactions; Tin alloys; Multifilamentary superconductors; Niobium base alloys; Asymmetry; Phonon dispersion; Phonon mode; Density functional method; Applied load
• ISSN: 0953-8984; 1361-648X; 1361-648X
• DOI: 10.1088/0953-8984/25/13/135702

Using calculations from first principles based on density-functional theory we have studied the strain sensitivity of the A15 superconductor Nb3Sn. The Nb3Sn lattice cell was deformed in the same way as observed experimentally on multifilamentary, technological wires subject to loads applied along their axes. The phonon dispersion curves and electronic band structures along different high-symmetry directions in the Brillouin zone were calculated, at different levels of applied strain, , on both the compressive and the tensile side. Starting from the calculated averaged phonon frequencies and electron-phonon coupling, the superconducting characteristic critical temperature of the material, Tc, has been calculated by means of the Allen-Dynes modification of the McMillan formula. As a result, the characteristic bell-shaped Tc versus curve, with a maximum at zero intrinsic strain, and with a slight asymmetry between the tensile and compressive sides, has been obtained. These first-principle calculations thus show that the strain sensitivity of Nb3Sn has a microscopic and intrinsic origin, originating from shifts in the Nb3Sn critical surface. In addition, our computations show that variations of the superconducting properties of this compound are correlated to stress-induced changes in both the phononic and electronic properties. Finally, the strain function describing the strain sensitivity of Nb3Sn has been extracted from the computed Tc( ) curve, and compared to experimental data from multifilamentary, composite wires. Both curves show the expected bell-shaped behavior, but the strain sensitivity of the wire is enhanced with respect to the theoretical predictions for bulk, perfectly binary and stoichiometric Nb3Sn. An understanding of the origin of this difference might open potential pathways towards improvement of the strain tolerance in such systems.