THE EFFECT OF THE MAXIMUM PROCESSING TEMPERATURE ON THE MICROSTRUCTURE AND ELECTRICAL-PROPERTIES OF MELT-PROCESSED AG-SHEATHED BI2SR2CACU2OX TAPE

The critical current density (J(c)) is very sensitive to the maximum t emperature (T-m) used to melt process Ag-sheathed Bi2Sr2CaCu2Ox, tapes , In this study we have found that the optimum T-m, was 894-896 degree s C and that variations of +/-2 degrees C strongly decreased J(c), We found that the density of the oxide core and its Vickers hardness disp layed a maximum in tapes that had been processed at the optimum T-m. I n addition, the room temperature electrical resistivity of the core wa s lowest for the tapes with the maximum J(c) at 4.2 K. A formation of macropores was observed in tapes processed at T-m above the optimum on e, MO imaging and SEM observation showed that the magnetic flux penetr ates more easily into tape areas containing macropores. Together these observations show that T-m exerts a very powerful effect on the macro scopic density of the oxide core, this controlling the connectivity an d the effective cross-section of the oxide core. Thus J(c) depends on T-m primarily because the effective cross-section of the core depends on T-m.