Characterization of grain boundaries in YBa₂Cu₃O_y bicrystal junctions

I-V, V-O characteristics and atomic force images of grain boundary Josephson junctions fabricated on SrTiO, bicrystal substrates were investigated. The half integer Shapiro steps and I, versus B curves show evidence of the inhomogeneous current distribution along the grain boundary junction. The dc SQUID formed on the grain boundary shows the expected V-O curve. The AFM images, R-T curves and IeRn product reveal sequential destructive deterioration of the junction originating from the underlying grooved substrate. The results are discussed.