Grain-boundary structure and segregation in Nb3Sn coatings on Nb for high-performance superconducting radiofrequency cavity applications

Abstract

We report on atomic-scale analyses of grain boundary (GB) structures and segregation in Nb3Sn coatings on Nb, prepared by the vapor-diffusion process, for superconducting radiofrequency (SRF) cavity applications, utilizing atom-probe tomography, high-resolution scanning transmission electron-microscopy and first-principles calculations. We demonstrate that the chemical composition of Nb3Sn GBs is correlated strongly with the diffusion of Sn and Nb at GBs during the coating process. In a sample coated with a relatively large Sn flux, we observe an interfacial width of Sn segregation at a GB of ~3 nm, with a maximum concentration of ~35 at.%. After post-annealing at 1100 oC for 3 h, the Sn segregated at GBs disappears and Nb segregation is observed subsequently at GBs, indicating that Nb diffused into the Nb3Sn GBs from the Nb substrate. It is also demonstrated that the amount of Sn segregation in a Nb3Sn coating can be controlled by: (i) Sn flux; and (ii) the temperatures of the Nb substrates and Sn source, which may affect the overall kinetics including GB diffusion of Sn and Nb. An investigation of the correlation between the chemical compositions of GBs and Nb3Sn SRF cavity performance reveals that the Nb3Sn SRF cavities with the best performance (high-quality factors at high accelerating electric-field gradients) do not exhibit Sn segregation at GBs. Our results suggest that the chemical compositions of GBs in Nb3Sn coatings for SRF cavities can be controlled by GB engineering and can be utilized to optimize fabrication of high-quality Nb3Sn coatings for SRF cavities.

References in corpus (14)

• Weak-link behavior of grain boundaries in superconducting Ba(Fe1-xCox)2As2 bicrystals
• A review and prospects for Nb3Sn superconductor development
• What limits supercurrents in high temperature superconductors? A microscopic model of cuprate grain boundaries
• To use or not to use cool superconductors?
• Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields
• Superheating field of superconductors within Ginzburg-Landau theory
• Efficient expulsion of magnetic flux in superconducting RF cavities for high $Q_0$ applications
• Internally Oxidized Nb3Sn Strands with Fine Grain Size and High Critical Current Density
• Theoretical estimates of maximum fields in superconducting resonant radio frequency cavities: Stability theory, disorder, and laminates
• Analysis of Nb3Sn surface layers for superconducting RF cavity applications
• Atomic scale analysis of Nb3Sn on Nb prepared by a vapor-diffusion process for superconducting radiofrequency cavity applications
• Performance-defining properties of Nb${}_3$Sn coating in SRF cavities
• Dynamic transition of vortices into phase slips and generation of vortex-antivortex pairs in thin film Josephson junctions under dc and ac currents
• $\text{Ab Initio}$ Study of Antisite Defects in Nb${}_3$Sn: Phase Diagram and Impact on Superconductivity

Cited by in corpus (11)

• Advances in Nb3Sn superconducting radiofrequency cavities towards first practical accelerator applications
• Analysis of Magnetic Vortex Dissipation in Sn-Segregated Boundaries in Nb${}_3$Sn Superconducting RF Cavities
• Microwave measurements of the high magnetic field vortex motion pinning parameters in Nb${}_3$Sn
• Development of a prototype superconducting radio-frequency cavity for conduction-cooled accelerators
• $\text{Ab Initio}$ Study of Antisite Defects in Nb${}_3$Sn: Phase Diagram and Impact on Superconductivity
• $\text{Ab Initio}$ Theory of the Impact from Grain Boundaries and Substitutional Defects on Superconducting Nb${}_3$Sn
• Smooth, homogeneous, high-purity Nb3Sn superconducting RF resonant cavity by seed-free electrochemical synthesis
• Microscopic Examination of SRF-quality Nb Films through Local Nonlinear Microwave Response
• A Time-Dependent Ginzburg-Landau Framework for Sample-Specific Simulation of Superconductors for SRF Applications
• Microscopic Investigation of rf Vortex Nucleation in Nb3Sn Films Using a Near-Field Magnetic Microwave Microscope
• Microwave Vortex Motion Characterization of Nb${}_3$Sn Coatings for Applications in High Magnetic Fields