Critical current densities in single crystal Bi sub (2.2) Sr sub 2 Ca sub (0.8) Cu sub 2 O sub (8+delta).

We report transport and magnetic measurements of critical current densities in single crystals of high T sub c superconductors in the Bi-Sr-Ca-Cu-O system. Transport measurements of J sub c were made using a pulse method, while a vibrating sample magnetometer was used to measure M-H loops of oriented crystals in fields up to 15 kOe. The transport critical current at 77K in zero field is greater than 4 X 10 sup 4 A/cm sup 2. Values for transport J sub c in zero applied field are higher than those of Ba sub 2 YCu sub 3 O sub 7 single crystals at comparable temperatures, which is evidence that twins are not necessary for high J sub c values. Also we observe a strong magnetic field dependence for J sub c at temperatures above ~20K.