Superconducting MgB2 films were prepared on differently oriented α-Al2O3 substrates, C- and R-planes, which yielded superconducting transition temperatures of about 28K. The electric resistivity of the MgB2 film deposited on an R-plane substrate was 300µΩcm, six times larger than that on a c-plane substrate, 50µΩcm. To understand these differences in the electrical properties, transmission electron microscopy was used to carry out a structural and the compositional analysis. It was shown from selected-area electron diffraction patterns that the microstructure consisted of a mixture of columnar MgB2 grains and amorphous phases in the case of the R-plane specimen, while no amorphous phase was present in the case of the C-plane specimen.

Structural and Analytical Characterization of As-Grown MgB2 Film Sputtered on Differently Oriented α-Al2O3 Substrate. W.J.Moon, K.Kaneko, S.Toh, M.Saunders, A.Saito, Z.Wang, H.Abe, M.Naito: Superconductor Science and Technology, 2005, 18, 92-100