Annealing study on the properties of Cu-based Nb3Sn films under argon pressures for SRF applications

Abstract Nb3Sn is an alternative material for future superconducting accelerators. With its higher critical temperature and superheating field than that of niobium, its application in the field of SRF is a great advantage. In this paper, the magnetron sputtering method is applied to prepare the Nb3Sn thin film on the oxygen-free copper substrate by the stoichiometric target—the ratio of 3:1 of niobium to tin, so as to explore the effect of different annealing air pressures on the properties of the film in detail. The film crystal structure, morphology, composition, and superconducting critical temperature were characterized by XRD, SEM, EDS, and MPMS. After in-situ annealing, XRD and MPMS reveal the existence of Nb3Sn crystal. The compact film with good surface properties is free of cracks and tin islands. The superconducting critical temperature reaches 13.6 K. The results show that if annealing was conducted in Ar atmosphere at 1 Pa, the obtained film exhibits better performance with a sharp transition from the superconducting state to the normal state.