EFFECT OF GROWTH-CONDITIONS ON THE PROPERTIES AND MORPHOLOGY OF CHEMICALLY DERIVED EPITAXIAL THIN-FILMS OF BA2YCU3O7-X ON (001) LAALO3

Epitaxial thin films of Ba2YCu3O7-x (BYC) were prepared on (001) LaAlO3 single-crystal substrates by metalorganic deposition of metal trifluoroacetate precursors. This is an ex situ process that requires high-temperature annealing in a humid atmosphere to produce stoichiometric BYC thin films. The chemically derived superconducting films were found to have high critical temperatures and high current densities when crystallized under low-oxygen partial pressures. Superconducting films of 70 nm thickness with zero-field critical current densities greater than 5 x 10(6) A/cm2 at 77 K and zero resistance at 92 K were prepared by annealing at 780 and 830-degrees-C in 2.5 x 10(-4) to 1 x 10(-3) atm oxygen furnace atmospheres. As the film thickness was increased, the superconducting properties and surface smoothness of the films tended to degrade. This behavior was consistent with a microstructural model in which the films are composed of a dense slab of c-axis normal BYC near the film/substrate interface with the overlying material dominated by grains with c-axis in-plane crystallographic orientation. The transport J(c) fell to 2-3 x 10(6) A/cm2 for films of 200-250-nm thickness annealed at 780-degrees-C in 1 x 10(-3) atm oxygen. As the P(O2) was raised to 0.032 atm at 780-degrees-C, for films of the same thickness, the J(c) at 77 K decreased to 0.7 x 10(6)-1 x 10(6) A/cm2 and the T(c)(R = 0) dropped to 89 K. Increasing the furnace P(O2) was also found to degrade the crystalline quality of the films, as characterized by ion channeling Rutherford backscattering spectroscopy.