OPTIMIZATION OF THE PREPARATION PARAMETERS OF MONOFILAMENTARY BI(2223) TAPES AND THE EFFECT OF THE ROLLING PRESSURE ON J(C)

The transport critical currents of Ag-sheathed Bi(2223) tapes produced by rolling have been improved by an optimization of some crucial parameters of the tape fabrication process. New results about the correlations between the critical current density and the powder heat treatment temperature and time, the cold deformation steps, as well as the tape heat treatment temperature and time are presented. Moreover, among all the previously cited parameters, we have found that the pressure exerted on the tapes during the rolling deformation between the heat treatments has a strong influence on the transport properties: a maximum j(c)(77 K, 0 T) value of 30 kA cm(-2) (averaged over the whole oxide cross section) on rolled Bi(2223) tapes was found for a rolling pressure of 0.6 GPa. At higher pressures, the formation of transverse cracks in the filament limits the critical current. A comparison between tapes of the same type, prepared either by rolling or by passing procedures, shows that the latter reach higher j(c)(77 K, 0 T) values (between 37 kA cm(-2) and 43 kA cm(-2)) due to the possibility of applying higher pressures (2 GPa) without the formation of cracks.