Doping effect at grain boundary of YBa2Cu3O7−y (YBCO) was studied by doping a variety of elements, including Ca, Fe, and Ag, etc. It was observed that the dopants preferentially occupy the grain boundary region and have different effects on the super-current transport through the grain boundary. The concurrent doping of Ca and Ag was found to further improve the grain boundary transparency to the super-current in YBCO, compared to the individual doping effect of Ag or Ca.

Repair of Grain Boundary by Preferential-Doping in YBa2Cu3O7−y. C.H.Cheng, Y.Zhao: Physica C, 2007, 463-465, 174-7