Surface degradation of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superconductors on exposure to air and humidity

Surface modifications from exposure of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ pellets and thin films of the 1:2:3 composition to ambient atmosphere and 85% relative humidity at 50 °C were measured using x-ray photoelectron spectroscopy and scanning Auger electron multiprobe. Surface formation of ${\mathrm{BaCO}}_3$ and Ba(OH${)}_2$ was detected. The surface layer of the sintered pellets did not have any Cu after 48 h of moisture treatment. The degradation in the thin-film samples was substantially less. The rate of degradation appears to be controlled by grain-boundary diffusion.