The impact of Cu/Sn precursor tin content on the properties and growth mechanism of Nb₃Sn thin films via bronze methods

Abstract This study systematically investigates the effect of Cu/Sn precursor tin content on the growth mechanism and superconducting properties of Nb 3 Sn coatings synthesized using the electrochemical and thermal synthesis (ETS) bronze methods. The ETS process entails annealing Cu/Sn coatings at 210 °C and 400 °C to form bronze alloy precursors, which are then annealed at 700 °C to form Nb 3 Sn coatings on Nb surfaces. To evaluate the effect of tin content, Cu/Sn coatings with varying tin concentrations were coated onto Nb substrates. The results highlight the critical role of tin content in determining the characteristics of Nb 3 Sn. Specifically, a high tin content (>20 at%) leads to a decrease in critical temperature ( T c ) and an increase in transition width (Δ T c ), accompanied by the formation of insoluble niobium oxide impurities. Conversely, precursors with a moderate tin content (15–20 at%) are found to be optimal for Nb 3 Sn coating applications in superconducting radio frequency (SRF) technology. Furthermore, this study delves into the one-dimensional diffusion process that governs the growth of Nb 3 Sn coatings during high-temperature heat treatment. By calculating the growth exponent and diffusion coefficient of the Nb 3 Sn coatings, we demonstrate that the growth mechanism of Nb 3 Sn encompasses both grain boundary diffusion and interface reaction. Overall, the experimental findings and growth kinetics presented in this study establish a foundation for future research and applications aimed at advancing Cu-based Nb 3 Sn thin film SRF (TFSRF) cavities.