EPITAXIAL YBA2CU3O7 GROWTH ON KTAO3 (001) SINGLE-CRYSTALS

Epitaxial films of YBa2Cu3O7 have been grown on KTaO3 (100) single-crystal substrates by means of reactive thermal coevaporation at temperatures between 560 and 750-degrees-C. The orientation of the YBa2Cu3O7 crystallographic c axis in these films was perpendicular to the substrate surface throughout the complete range of deposition temperatures even 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 growth of YBa2Cu3O7 films are known to be relatively sensitive to the formation of a-axis-oriented grains at imperfections on the substrate material, an investigation of the influence of the substrate surface finish on the film properties was carried out. Using substrates with appropriately prepared surfaces, YBa2Cu3O7 films exhibited a high degree of crystalline perfection, zero resistance at temperatures of 89 K and critical current densities up to 3 X 10(6) A/cm2.