  Grain boundaries (GBs) of YBa2Cu3Oy (YBCO) are preferentially doped with Ag
by the solid-state diffusion method. The distribution of Ag is highly localized
in the GB. As a result of the Ag doping, the Jc-H behavior of YBCO textured
polycrystalline samples is significantly improved, and at 60 K and 7 T, Jc is
tripled. It is proposed that Ag could partially replace the Cu in CuO2 planes
near GBs, therefore reducing the geometric distortion of Cu-O bonds and making
the effective GBs thinner.
