Correlation between normal and superconducting transport properties of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ ceramic samples

We have studied normal and superconducting transport properties of nearly single phase Bi1.65Pb0.35Sr2Ca2Cu3O10+δ (Bi-2223) ceramic samples. The samples were prepared from the same batch obtained by solid-state reaction method and pressed uniaxially at different compacting pressures ranging from 90 to 600 MPa before the last heat treatment. We have found by using magnetization versus applied magnetic field measurements, performed in powder samples, that both the lower critical field H clg ∼ 80 Oe and the full penetration field H* ∼ 135 Oe of grains at 77 K are similar in all samples. From electrical resistivity measurements as a function of temperature, we were able to separate contributions arising from both the grain misalignment and microstructural defects. The results suggest that the grain orientation and the connectivity between grains are improved with increasing compacting pressures. It was found that the superconducting critical current density in zero applied magnetic field J c(0) measured in our samples increases from 58 A/cm2 to 418 A/cm2. The normalized critical current density dependence on applied magnetic field, J c(B a)/J c(0), has showed to be very sensitive to the compacting pressure: it exhibits a clear Josephson-like behavior at low compacting pressure, which changes to a more magnetic field independent behavior at higher compacting pressures. In addition, the flux-trapping curves of samples subjected to different compacting pressure have revealed the presence of three superconducting levels: the superconducting grains, the superconducting clusters, and the weak links. A correlation between the normal and superconducting transport properties of these materials is discussed based on their dissipation mechanisms