Nb3Sn films on sapphire - a promising alternative for superconductive microwave technology

Phase-pure, large grained Nb3Sn films on sapphire substrates have been prep ared by a tno-step process, The average gain size increased with the film t hickness. Transport properties like the penetration depth, mean free path, and critical current density have been investigated in relation to the micr ostructure of the films. Measurements of the DC- and HF-magnetic field depe ndent surface impedance were performed. Nonlinear surface resistance occurr ed at field le, els above B-s = 25mT, and was related to extrinsic mechanis ms, The relevance of weak coupling at gain boundaries decreased with increa sing grain size. Thus heating at local defects was concluded to be the domi nant limiting mechanism in large grained films. An intrinsic field limit of B-cl = 140mT was found. The polycrystalline films showed a much lower resi dual resistance and comparable power handling compared to high-quality epit axial YBa2Cu3O7-delta-films.