Study of micron-thick MgB2 films on niobium substrates

Abstract

1 µm thickpolycrystalline MgB2 films have been grown on commercial niobium sheets using the hybrid physical–chemicalvapour deposition technique (HPCVD). Their zero-resistance transition temperatureTc0 ranges from 38 to 39 K and the transition temperature widthΔTc is about 0.1–0.2 K. The films are composed of regular plate-shapedMgB2 crystallites and have lattice constants about the bulk values. Some diffusion regions wereobserved at the interface between the film and the substrate by a line scanning spectra ofenergy-dispersive x-ray spectroscopy (EDX) on the cross section, which might enhancethe adhesion of the coated layer to the substrate. The critical current densities,Jc, of these films, calculated by the Bean model, are greater than5 × 106 A cm−2 at 10 K in zero field. Although tiny cracks in the film were created bybending 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 samplehas a certain ductibility.