Antisite defects play a critical role in Nb3Sn superconducting radio frequency (SRF) cavity physics. Such defects are the primary form of disorder in Nb3Sn, and are responsible for stoichiometry variations, including experimentally observed tin-depleted regions within grains and tin-rich regions around grain boundaries. But why they cluster to form regions of different stoichiometries and how they affect the SRF properties of Nb3Sn cavities are not fully understood. Using ab initio techniques, we calculate the A15 region of the Nb-Sn phase diagram, discuss a possible modification to the phase diagram near grain boundaries, and calculate Tc as a function of stoichiometry, including experimentally inaccessible tin-rich stoichiometry. We find that the impact of antisite defects on the density of states near the Fermi-level of Nb3Sn plays a key role in determining many of their properties. These results improve our understanding of the obstacles facing Nb3Sn SRF systems, and how modified growth processes might overcome them.
@article{arxiv.1912.07576,
title = {$\textit{Ab Initio}$ Study of Antisite Defects in Nb$_3$Sn: Phase Diagram and Impact on Superconductivity},
author = {Nathan S. Sitaraman and Jared Carlson and Alden R. Pack and Ryan D. Porter and Matthias U. Liepe and Mark K. Transtrum and Tomás A. Arias},
journal= {arXiv preprint arXiv:1912.07576},
year = {2021}
}