Influence of Ag-Au and Ag-Cu alloys on Bi2Sr2CaCu2Ox superconductor

The influence of Ag-Au and Ag-Cu alloy substrates on the microstructure and superconducting properties of Bi2Sr2CaCu2Ox (Bi-2212) was studied. The critical current density (Jc) of Bi-2212/(Ag-Au) was not degraded by increasing the Au content of the Ag-Au alloy, while the Jc of Bi-2212/(Ag-Cu) was drastically degraded by increasing the Cu content of the Ag-Cu alloy. The microstructure of Bi-2212 on the Ag-Au alloy was uniform and no precipitates were observed. The Jc degradation of Bi-2212 in contact with the Ag-Cu alloy was understood by the fact that Cu absorption of Bi-2212 from the Ag-Cu alloys changed the composition of the oxide layer. Ag-Au alloys are superior substrate materials for Bi-2212 for power current leads for superconducting magnets, taking into account their low thermal conductivity.