EFFECT OF SILVER SOLUBILITY ON MICROSTRUCTURE AND SUPERCONDUCTING PROPERTIES OF YBA2CU3-XAGXO7-DELTA SUPERCONDUCTORS

The effect of silver (Ag) solubility on microstructure and superconducting properties of YBa2Cu3-xAgxO7-delta (0 less-than-or-equal-to x less-than-or-equal-to 0.5) superconductors has been evaluated. The solubility limit of Ag for copper sites in YBCO at ambient conditions (room temperature, atmospheric pressure) was evaluated to be x congruent-to 0.06. Analysis revealed the Ag content (x) of YBCO grains to be lower than the nominal Ag content (x(n)) used for fabrication, probably due to processing-related problems. Part of the Ag used for fabrication segregates on the YBCO grain boundaries. The segregated Ag particles are believed to pin YBCO grains, resulting in fine-grain microstructures. For low nominal Ag content, x(n) < 0.2, critical current density (J(c)) increased from 98 to 160 A/cm2 as a function of increasing Ag content. These improvements are believed to be due to the increased oxygen content and associated microstructural changes in the YBCO. For higher nominal Ag content, x(n) > 0.2, however, J(c) decreased rapidly with the increasing Ag content due to the precipitation of nonsuperconducting phases.