Repair of grain boundary by preferential-doping in YBa2Cu3O7−y

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 supercurrent transport through the grain boundary. The concurrent doping of Ca and Ag has been found to further improve the grain boundary transparency to the supercurrent in YBCO, compared to the individual doping effect of Ag or Ca.