Abstract
In the present study, the local atomic structure of a Nb3Sn superconductor sample has been probed by X-ray absorption fine structure (XAFS) as a function of hydrostatic pressure (from ambient up to 26 GPa) using a diamond anvil cell set-up. The analysis of the Nb-K edge extended X-ray absorption fine structure (EXAFS) data was carried out combining standard multi shell structural refinement and reverse Monte Carlo method to provide detailed in situ characterization of the pressure-induced evolution of the Nb local structure in Nb3Sn. The results highlight a complex evolution of Nb chains at the local atomic scale, with a peculiar correlated displacement of Nb–Nb and Nb–Nb–Nb configurations. Such a local effect appears related to anomalies evidenced by X-ray diffraction in other superconductors belonging to the same A15 crystallographic structure.
Highlights
Nb3Sn is a brittle intermetallic material belonging to the class of the A15 compounds that in 1954 reached a superconducting transition temperature of Tc ≈ 18 K [1]
The multiple scattering (MS) analysis could be a difficult task using standard extended X-ray absorption fine structure (EXAFS) methods based on the multi-shell data refinement due to Provost et al [54]: i. increasing number of required parameters; ii. increasing correlations among the structural parameters; iii. the failure of the small harmonic disorder model [41] and the occurrence of correlated disorder in SS and MS shells [41,55]
The local atomic structure around Nb in Nb3Sn has been characterized in situ between ambient pressure and 26 GPa by X-ray absorption spectroscopy (XAS)
Summary
Nb3Sn is a brittle intermetallic material belonging to the class of the A15 compounds (space group Pm-3n) that in 1954 reached a superconducting transition temperature of Tc ≈ 18 K [1]. Even more important, is its capability to carry high current densities Jc > 103 A/mm2 [2], allowing to make compact magnets reaching high critical fields Bc2 up to 30 T [3,4], essential for high field superconductor applications. Less is known about the structural modifications induced by pressure, especially on the crystallographic and atomic scale [15,16,17] These informations are crucial for achieving accurate model of the Nb3Sn properties. Accurate models require deep knowledge about the atomic structure at the crystallographic and atomic (local) scale
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