The effect of the maximum processing temperature on themicrostructure and electrical properties of melt processed Ag-sheathedBi2Sr2CaCu2Ox tape

摘要

The critical current density (Jc) is very sensitive to the maximum temperature (Tm) used to melt process Ag-sheathed Bi2Sr2CaCu2Ox tapes. In this study we have found that the optimum Tm was 894-896°C and that variations of ±2°C strongly decreased Jc. We found that the density of the oxide core and its Vickers hardness displayed a maximum in tapes that had been processed at the optimum T m. In addition, the room temperature electrical resistivity of the core was lowest for the tapes with the maximum Jc at 4.2 K. A formation of macropores was observed in tapes processed at T m above the optimum one. MO imaging and SEM observation showed that the magnetic flux penetrates more easily into tape areas containing macropores. Together these observations show that Tm exerts a very powerful effect on the macroscopic density of the oxide core, this controlling the connectivity and the effective cross-section of the oxide core. Thus Jc depends on Tm primarily because the effective cross-section of the core depends on Tm