Effect of phase assemblage of precursor on the fabrication process and properties of Bi2223 tape sheathed with Ag-alloy

The use of alloy sheath is effective to increase the strength of Ag-sheathed Bi2223 tapes. However, the J_c value of alloy sheathed tapes was not high enough since the undesired reaction to form impurity phases and the change in formation rate of Bi2223 were disturbed by the microstructure of the filaments . In this study, the effect of 2223 contents in precursor on the formation and property of Bi2223 tapes sheathed with Ag-Mg alloy was investigated. The conversion rate of Bi2223 from Bi2212 was increased by the addition of Bi2223 phase in precursor but the conversion rate in Ag-Mg alloy sheathed tapes was slower than that in the Ag-Cu alloy sheathed tapes. This reduction of conversion speed of Bi2223 may be attributed to the decrease in the growth rate of Bi2223 crystals in Ag-Mg alloy sheath. Since the tapes with small Bi2223 crystals after first sintering showed many outgrowths after final sintering, the formation of outgrowth would be caused in the case of small crystal size. The J_c value of 2.2 x 10⁴ A/cm² was achieved in the samples using the precursor with 10 wt.% 2223. The high J_c value can be achieved by the proper control of precursor condition including the contents of Bi2223 and corresponding heat treatment pattern in Ag-Mg alloy sheathed tapes