Influence of growth conditions and weak fields on the electrical properties of the vortex and superconducting states of Bi2Sr2CaCu2Ox thick tapes

A systematic investigation of the electrical parameters of Bi2Sr2CaCu2Ox thick tapes in the vortex and superconducting states was carried out. The tapes were grown on either single crystals of MgO or silver foil under different heat treatment conditions. The temperature dependence of the electrical resistivity in the vortex state was found to follow an Arrhenius-like relation of the form ρ(T, H) = ρ0exp(−U0(H)/kBT). The activation energy, U0, showed a strong dependence on the applied field and the growth conditions of the sample. Its average values were between 10 and 300 meV. The current–voltage characteristics (I–V) for various samples of different growth conditions and applied fields were also investigated. The study revealed a current dependence on the applied voltage was found to fit a power law of the form: I ∼ Vα, where α is an exponent whose values are strongly dependent on growth conditions. At constant voltages, the current was found to decrease exponentially with the applied magnetic field according to I(B) ∼ exp(−cB/B∗), where c is a constant depending on growth conditions and B∗ is a characteristic field of the sample. This exponential decay of the current is attributed to strong flux pinning centers. The dependence of the current on field and voltage could be written as I ∼ Vαexp(−cB/B∗). Furthermore, the heat treatment conditions and annealing atmosphere had strong influence on the I–V characteristic of the sample.