Superconducting MgB2 films via precursor postprocessing approach

Superconducting MgB2 films with Tc=38.6 K were prepared using a precursor-deposition, ex situ postprocessing approach. Precursor films of boron, ∼0.5 μm thick, were deposited onto Al2O3 (102) substrates by electron-beam evaporation; a postanneal at 890 °C in the presence of bulk MgB2 and Mg metal produced highly crystalline MgB2 films. X-ray diffraction indicated that the films exhibit some degree of c-axis alignment, but are randomly oriented in plane. Transport current measurements of the superconducting properties show high values of the critical current density and yield an irreversibility line that exceeds that determined by magnetic measurements on bulk polycrystalline materials.