EPITAXIAL YBA2CU3O7 GROWTH ON KTAO3 (001) SINGLE-CRYSTALS

Epitaxial films of YBa2Cu3O7 have been grown on KTaO3 (100) single-cry stal substrates by means of reactive thermal coevaporation at temperat ures between 560 and 750-degrees-C. The orientation of the YBa2Cu3O7 c rystallographic c axis in these films was perpendicular to the substra te surface throughout the complete range of deposition temperatures ev en though the KTaO3 lattice constant represents a better match to the YBa2Cu3O7 c axis than to the a and b axes. Since the nucleation and gr owth of YBa2Cu3O7 films are known to be relatively sensitive to the fo rmation of a-axis-oriented grains at imperfections on the substrate ma terial, an investigation of the influence of the substrate surface fin ish on the film properties was carried out. Using substrates with appr opriately prepared surfaces, YBa2Cu3O7 films exhibited a high degree o f crystalline perfection, zero resistance at temperatures of 89 K and critical current densities up to 3 X 10(6) A/cm2.