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Study of micron-thick MgB2 films on niobium substrates

1 µm thick polycrystalline MgB2 films have been grown on commercial niobium sheets using the hybrid physical–chemical vapour deposition technique (HPCVD). Their zero-resistance transition temperature Tc0 ranges from 38 to 39 K and the transition temperature width ΔTc is about 0.1–0.2 K. The films are composed of regular plate-shaped MgB2 crystallites and have lattice constants about the bulk values. Some diffusion regions were observed at the interface between the film and the substrate by a line scanning spectra of energy-dispersive x-ray spectroscopy (EDX) on the cross section, which might enhance the adhesion of the coated layer to the substrate. The critical current densities, Jc, of these films, calculated by the Bean model, are greater than 5 × 106 A cm−2 at 10 K in zero field. Although tiny cracks in the film were created by bending the sample on a curved surface with a radius of 1.4 mm, however, Tc0 of the bent film was not affected and remained about 39 K, which indicates that the sample has a certain ductibility.