The Effect of Hydrostatic Pressure on the Superconducting and Structural Properties of Nb 3Sn: Ab-initio Modeling and SR-XRD Investigation

We report on the investigations of the structural and superconducting properties of Nb3Sn in the GPa range by angular dispersive synchrotron X-ray diffraction and ab-initio calculations based on density functional theory. X-ray Diffraction experiments were carried out on Nb3Sn technological samples to explore the equation of state at room temperature and at pressures up to 43.5 GPa: We observe an anomaly in the P-V curve in the region 5-10 GPa. The ab-initio calculated lattice parameter of Nb3 Sn as a function of pressure has been used as an input for the calculation of the phonon dispersion curves and of the electronic band structures along different high-symmetry directions in the Brillouin zone. The critical temperature has been calculated as a function of the hydrostatic pressure by means of the Allen-Dynes modification of the McMillan formula: We found that its behavior is dictated mostly by the electronic contribution, but evident anomalies up to 6 GPa arise from phonons. These findings are a clue that Nb3 Sn could have some structural instabilities with impact on its superconducting properties when subjected to a pressure of a few GPa and they represent an important step to understand and optimize the performances of Nb3Sn materials under the hard operational conditions of high field superconducting magnets.