Electrical conduction and surface acoustic wave attenuation in a granular YBa2Cu3O7-y film

Measurements of sheet resistance and surface acoustic wave (SAW) attenuation were performed on a granular film of the high temperature superconductor YBa₂Cu₃O_7-y (YBCO) deposited on a piezoelectric (LiNbO₃) substrate. Measurements were first performed soon after the film was produced, and repeated after three years aging in air. The resistive behavior, as measured by a four-probe method, was found to have changed significantly with aging, whereas little or no change was observed in the behavior of the SAW attenuation. It will be shown that these two results are not contradictory. A model for an average inter-grain junction is developed which agrees quantitatively with the resistance data. Using the same model, the resistance of square random resistor networks of various sizes are calculated yielding a qualitative agreement with the SAW data