Structural and electrical properties of the Y-Ba-Cu-O superconducting films prepared by spray pyrolysis

High-Tc superconducting YBCO thin films have been grown on (100) MgO substrates by a chemical spray pyrolysis method. The as-sprayed films were amorphous and insulating, but upon annealing the films became superconducting and show a textured surface morphology with an average grain size of the order of 5-15 microns. The films were highly oriented with the c-axis being perpendicular to the substrate surface. Three different microstructures were recorded: long rod-shaped grains, platelet or rounded-shape grains, and a melting-like growth. The onset transition temperature was around 83-86 K, and the completion of the transition to zero resistance was in the range 73-78 K. The magnitude of the measured critical current density was in the range 750-3750 A/sq cm at 30 K. A correlation between the resistance of the tunneling junctions and the critical current density was found from the theoretical models.