Fabrication, characterization, and theoretical analysis of high-T c Y-Ba-Cu-O superconducting films prepared by a chemical sol gel method

Thin films of Y1Ba2Cu3O7−x have been produced on MgO substrates by a chemical sol gel method. X-ray diffraction data indicate that the annealed films have the characteristic orthorhombic structure with lattice constants which are nearly the same as the values reported for the bulk specimen of Y1Ba2Cu3O7−x. Auger electron spectroscopy depth profiling measurements indicate that the films are uniform in thickness and composition. Measurements of electrical resistance of films 1–4.7 μm in thickness have been carried out between 12 and 300 K using a standard four-probe geometry. The films are superconducting with an onset temperature around 95 K and a full transition temperature as high as 79.5 K, and a critical current density of 2700 A/cm2 at 20 K. A theoretical analysis of the critical current density in Y1Ba2Cu3O7−x as a function of temperature has been made in order to determine the characteristics of the junctions between the superconducting grains. Theoretical models which describe the dependence of the critical current density on temperature have been presented and agreement has been found between these models and experimental values for sol gel films. The critical transport current has a temperature dependence which is characteristic of superconductor-normal metal-superconductor (S-N-S) type junctions. The magnitude of the resistance and thickness of the junctions has been determined from the theoretical models. Information regarding calculation of the oxygen content in Y1Ba2Cu3O7−x films is also presented.