Crystal Structure and Superconductivity of MgB2 Thin Films Grown on Various Oxide Substrates

The crystal structure and superconductivity of MgB2 thin films grown on various oxide substrates were investigated by X-ray diffraction and resistance measurement. The films were prepared by a two-step method, in which precursors B films were annealed in Mg vapor at 900○C. The X-ray diffraction shows that the MgB2 films grown on C–AL2O3, R–AL2O3, and MgO (001) are c-axis oriented while the films grown on SrTiO3 (001), LaAlO3 (001), and ZrO2 (001) are aligned with the (101) direction normal to the substrate planes. All the grown films show superconductivity and their transition temperature varies with the substrates in the range of 34–39 K. We think that the transition temperature variation is probably due to the lattice matching between the film and the substrate, as well as the interdiffusion at the film/substrate interface. The experimental results suggest that if there is no severe interdiffusion at the film/substrate interface in the high temperature annealing process, more substrates could be used for the growth of MgB2 films using the two-step method.