Speaker
Description
Here, we evaluate two co-sputtered compounds: Nb–Zr and Nb–Sn–Zr, as prospective superconducting materials for future RF cavity fabrication. We have studied how the crystal lattice structures, surface and bulk morphologies, oxidation states, and superconducting properties modify with variable Zr fraction, to determine the most useful range of Zr inclusions in these compounds for SRF applications.
In the first study, a variable content of Zr was introduced along with Nb and Sn during co-sputtering process, which resulted in Nb₃Sn matrix consisting of phase-separated ZrO₂ precipitates of 20 to 100 nm after annealing. Increasing the Zr concentration substantially reduced both the density and average dimensions of surface and bulk voids in Nb₃Sn thin film. We also observed that increasing the Zr content up to an optimal level can improve the superconducting transition temperature (T$_c$) and upper critical magnetic field (H$_{c2}$). In addition, higher Zr concentrations appeared to reduce oxygen diffusivity in the films, resulting in the formation of a thinner primary surface oxide layer.
In case of the Nb–Zr system, room-temperature co-sputtering directly produced single-phase bcc Nb-Zr alloys without the requirement of any post-annealing process. The resulting films also exhibited a preferred out-of-plane crystallographic orientation along the Nb (110) plane. Both the T$_c$ and H$_{c2}$ values increased monotonically with increasing Zr content up to approximately 15%; beyond this concentration, however, both properties began to degrade.
Our results suggest that Zr inclusion in sputtered Nb and Nb₃Sn coatings is promising for SRF applications, particularly for cavities operating in presence of high magnetic fields of several Tesla.