Critical current densities for the high temperature ceramic superconductors YBa/sub 2/Cu/sub 3/O/sub 7/ and Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+ delta

A pulsed transport technique has been used to measure the zero-field critical current densities of YBa/sub 2/Cu/sub 3/O/sub 7/ ceramic superconductors prepared under different sintering conditions. This low duty-cycle, pulsed technique, used on specially prepared samples with low-resistance current contacts, allows one to determine the entire superconducting/normal phase boundary without the problems associated with sample heating. The results can be interpreted in terms of two different critical-current densities. The intergrain critical current is low and is limited by the weak links between the grains; the intrinsic intragrain critical current is greater than 10/sup 4/ A/cm/sup 2/ at 77 K. Critical-current values inferred from magnetic hysteresis measurements made on the same samples agree with the intrinsic intragrain critical currents obtained using the pulsed transport technique. In addition, the magnetization-derived critical-current density has been determined for the high T/sub c/ phase Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+ delta / at 77 K.< >