Effects of silver doping on the superconducting YBaCu oxide

The doping effects of Ag on the ceramic body of YBaCu oxide have been studied. Two kinds of specimens were investigated, nominally, YBa2Cu3O7−δ +Ag (Ag-added) and YBa2Cu3−xAgxO7−δ (Ag-substituted), for their structural and super-conducting properties. It was found that Cu cations were not completely substituted by Ag ions even in the Ag-substituted specimens, and the excess metallic Ag filled the pores of the bulks in all cases. The excess Ag in the pores promoted a liquid phase sintering process that encouraged the formation of grains in shape of stacked large flat rectangular platelets and, hence, resulted in C-axis preferred orientation. The Tc was almost unchanged in the Ag-added specimens but decreased in the Ag-substituted specimens with x values larger than 0.1 mole fraction due to Cu-deficiency. In both kinds of specimens, the Jc were improved by the Ag-doping in the YBCO ceramics up to a certain amount of Ag, above which the appearance of semiconducting phases degraded the superconducting properties of the material.