INDUCTIVE MEASUREMENTS OF VOLTAGE-CURRENT CHARACTERISTICS BETWEEN 10(-12)V/CM AND 10(-2)V/CM IN RINGS OF BI2212 CERAMICS

A novel inductive method to determine the voltage-current characteristics in ring shaped superconductors is presented. The method allows one to measure unambiguously the intergranular currents and to vary the electric field E between 10(-12) V/cm and 10(-2) V/cm. It was applied to melt processed Bi2212 ceramics at temperatures between 10 K and 80 K and in magnetic fields up to 6 T. In the whole investigated H-T-E-region the power law E=E0 [j/j0(H, T)]alpha(H,T) is approximately obeyed. The field and temperature dependence of the experimental values of alpha can be fitted by alpha(H, T) = 100 T H-1exp[-9.2T/T(c)]. The experimental findings are compared with the predictions of various pinning theories.