Polycrystalline MgB2 films with a thickness of about 1µm were prepared at ambient pressure. The B layers were deposited onto single-crystalline and polycrystalline Al2O3 by screen printing, by airbrush techniques or by painting, followed by a reaction with Mg vapour. Grinding, mechanical and electrolytic polishing in non-aqueous dimethyl sulfoxide significantly improved the surface smoothness of the samples. The films had transition temperatures, TC(0), of 35K and irreversibility fields of up to 15T at 5K. Transport critical current densities of 3 x 108A/m2 were measured at 20K and 1T for MgB2 films on single-crystalline Al2O3, whereas 8 x 108A/m2 was found for films on polycrystalline Al2O3 under the same conditions. Magnetization data and magneto-optical imaging indicated instabilities (flux jumps) at 4.2K, which disappeared at around 10K. The critical current densities of all MgB2 films on either single-crystalline or polycrystalline Al2O3 were independent of the orientation of the film with respect to the magnetic field direction.

Preparation and Characterization of Superconducting MgB2 Films on Alumina. M.Kühberger, G.Gritzner, K.R.Schöppl, H.W.Weber, Å.A.F.Olsen, T.H.Johansen: Superconductor Science and Technology, 2004, 17, 764-9