Limiting factors for critical current densities in Bi2Sr2Ca2Cu3O10-Ag composite superconducting tapes at elevated temperatures

Detailed measurements of I-V curves at 4.2, 65, and 77 K as a function of applied magnetic field for two Bi(2:2:2:3)/Ag tapes, having critical current densities Jc of ∼1 and ∼2x104 A/cm2 (at 77 K and 0 T), revealed that (1) the primary limiting factor for the transport critical current densities in these tapes is the presence of a large fraction of weak and/or nonsuperconducting grain boundaries; (2) the observed dissipative voltages are due, however, mostly to the motion of the magnetic vortices in the grains; and (3) the E-J curves are well described by an expression, E∼exp[-(J0/J)μ], rather than the commonly used power law, i.e., E∼Jn, where μ, J0, and n are constants