Experimental study of microstructure and critical current density of YBCO Ag thick films under silver addition and electron irradiation

Thick polycrystalline films of silver doped YBCO were produced by the standard screen printing method and irradiated with a source of electrons at 1000 kGy. The critical temperature (T-c), the zero resistance temperature (T-0), the broadening of the superconductor transition and normal resistance, measured at 298 K, changed substantially in the irradiated sample when compared to the non-irradiated specimen. A detailed study using Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) on the cross sectional surface of the films revealed that silver was distributed in small amounts at the grain boundaries while some regions showed silver-rich-like clumps on the surface. In both cases, silver was found in a metallic state only. Such distribution was also confirmed by SEM images. We found by x-ray diffraction analysis important microstructural changes on the irradiated sample. The critical current density (J(c)) showed a sixfold increase after the sample was irradiated. The J(c) enhancing is directly associated with the increase in the flux pinning generated by the irradiation induced defects.