Grain boundary doping effect on critical current density in YBa2Cu3O7 polycrystalline materials

Abstract

Diffusion method has been developed to preferentially dope the grain boundaries (GBs) in textured YBa2Cu3O7 bicrystals and polycrystalline materials. Ag, Ca, Fe, Pb, etc. have been used as the dopants in this study. The distribution of the dopants is found to be highly localized around the GBs. The Jc of YBa2Cu3O7 textured polycrystalline samples are significantly enhanced by doping Ag or Ca in the GBs. The Ca doping effect has been explained by charge-carrier-compensation in the GBs, which reduces the GB/junction resistance and thus increases the GB critical current. The Ag doping effect has been explained by the partially repairing of the broken Cu–O bonds, which transforms an extended geometric distortion in CuO2 planes to a localized electronic distortion. Four mechanisms for repairing GB of HTSs are proposed, which are charge-carrier compensation, grain boundary cleaning, weak-link to pinning-center transformation, and concurrent doping.