Diffusion in A15 Nb3Sn: An atomistic study

Abstract

Detailed diffusion mechanism in the A15 Nb3Sn superconducting compound has been investigated using an atomistic simulation based on a newly developed interatomic potential for the Nb-Sn binary alloy system. In terms of volume diffusion, Sn atoms diffuse via Nb sites due to the structural feature of A15 Nb3Sn, and the calculated energetics shows that the diffusion of SnNb anti-site is easy whereas the formation of SnNb is rate determining. However, the calculated diffusivity shows that the experimentally observed growth kinetics of the Nb3Sn compound layer cannot be fully explained by volume diffusion. Grain boundary diffusion is predicted to be seven to fourteen orders of magnitude faster than the volume diffusion, which can sufficiently explain the known growth kinetics of the Nb3Sn layer. Accordingly, grain boundary diffusion is suggested as the governing diffusion mechanism in Nb3Sn. The fundamental understanding and the details of diffusion revealed in the present work will contribute to future studies for detailed analyzes of the alloying effects on the growth kinetics of the Nb3Sn compound.