Effect of alloying additions to Ag on thermal conductivity, electrical and mechanical properties of Ag-sheathed Bi-2223 tapes

Ag-sheathed Bi-2223 tapes were fabricated by a powder-in-tube technique with different configurations of the inner and outer sheath materials: Ag, Ag-Mg-Ni, Ag-Sb and Ag-Au. Characterization of thermal conductivity at 4.2 K to 100 K showed that the addition of Au decreased the thermal conductivity remarkably. The value at 40 K was 53.8 W/(m K) for AgAu-AgAu tape, five times lower than that of Ag-AgMgNi tape. The addition of Sb reduced AC losses much more than other alloyed element, partly due to its high electrical resistivity at 77 K. The measurement results of the normalized Ic dependence on magnetic field of the tapes indicated, however, no conclusive correlation between alloy type and Ic performance in field was highlighted. The mechanical property of alloy-sheathed tape was also evaluated. The sequence of the tapes' tensile strength from highest to lowest was: Ag-Mg-Ni, Ag-Sb, Ag-Au, Ag.