Critical Current Densities for the High Temperature Ceramic Superconductors YBa2Cu3O7 and Bi2Sr2Ca2Cu3O(10 + delta).

摘要

A pulsed transport technique has been used to measure the zero field critical current densities of YBa2Cu3O7 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 10000 sq cm at 77K. 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 (n=3) of the Bi2 Sr2 Ca (n-1) Cu(n)O(2n+4+delta) family at 77K. Keywords: Superconductivity; Ceramic; Thin films; Copper-oxides. Reprints. (JHD)