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

A pulsed transport technique has been used to measure the zero-field critical current densities of YBa(2)Cu(3)O (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(4) A/cm(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 < e1 > T < /e1 > (c) phase Bi(2)Sr(2)Ca(2)Cu(3)O(10 delta ) at 77 K