A transmission electron microscopy study was made of a MgB2/α-Al2O3 film that exhibited the typical property of a critical current density under magnetic fields. The MgB2 layer, 300nm in thickness, was grown onto a (001)α-Al2O3 substrate by using an in situ electron beam evaporation method. The JC of the film exhibited significantly high values when the applied magnetic field was perpendicular to the film surface. The MgB2 layer consisted of fine columnar MgB2 crystals which were 20 to 30nm in size. The columnar MgB2 crystals grew almost perpendicularly to the substrate surface and had no crystallographic orientation relationship with the α-Al2O3 substrate; because of an amorphous layer which formed first on the substrate. A high density of columnar grain boundaries within the MgB2 layer was expected to be effective for the enhancement of flux-pinning under a perpendicular magnetic field.

Relationship between Microstructure and JC Property in MgB2/α-Al2O3 Film Fabricated by in situ Electron Beam Evaporation. H.Sosiati, S.Hata, N.Kuwano, Y.Tomokiyo, H.Kitaguchi, T.Doi, H.Yamamoto, A.Matsumoto, K.Saitoh, H.Kumakura: Superconductor Science and Technology, 2005, 18, 1275-9