Effect of electric field relaxation on theV-Icurve

The effects of sweeping rate of applied current (d I /d t ) on the characteristic ( V - I ) and electric field relaxation ( V - t ) curves have been investigated numerically as well as experimentally. The calculation is based on the nonlinear electric field diffusion equation, while the experiment is conducted by electric transport measurements of V - I and V - t curves on three Ag-Bi-2223 tape samples. It is found that the V - I curves shift toward smaller current with increasing d I /d t and V decays with time apparently. We show that a certain d I /d t causes a highly spatially varied electric field which is the natural result of the fact that flux lines can only diffuse over barriers with certain velocity. We also show that the electric field diffusion causes the two phenomena in the bulk sample: (1) the V - I curve is affected by the sweeping rate of the applied current; (2) the resistance relaxes with time.