Improvement of mechanical properties of YBCO-Ag composite superconductors made by mixing with metallic Ag powder and AgNO₃ solution

The role of Ag additions in the microstructural evolution and related mechanical properties of YBCO has been studied. Various amounts of Ag have been added to YBCO by two different mixing techniques, i.e. in the form of metallic Ag powder and AgNO₃ solution. The strength and fracture toughness of YBCO specimen increased with increasing Ag content, probably because of strengthening mechanisms resulting from Ag addition. In addition, YBCO-Ag composites showed higher values of strength and fracture toughness when Ag was added in the form of AgNO₃ solution compared with those when it was added in the form of metallic Ag powder. Specifically, an addition of 10 vol% Ag, made by mixing with metallic Ag powder, increased strength from 88 to 116 MPa and fracture toughness from 1.6 to 2.6 MPa m^1/2. Corresponding improvements in strength and fracture toughness were 128 MPa and 2.9 MPa m^1/2, respectively, when YBCO was mixed with AgNO₃ solution. The better mechanical properties of the YBCO-Ag specimen mixed by the solution method are believed to be due to the microstructure of more finely and uniformly distributed Ag particles. Furthermore, addition of Ag did not have an adverse effect on the critical current density of YBCO superconductors.