Improvement of the intergranular pinning energy in uniaxially compacting (Bi-Pb)₂Sr₂Ca₂Cu₃O_10+δ ceramic samples

Abstract.

Measurements of the electrical resistivity as a function of temperature, ρ(T), for different values of applied magnetic field, B_a (0 ≤ B_a ≤ 50 mT), were performed in polycrystalline samples of Bi_1.65Pb_0.35Sr₂Ca₂ Cu₃O_10+δ subjected to different uniaxial compacting pressure (UCP). We have found appreciable differences in the grain orientation between samples by using X-ray diffractometry. From the X-ray diffraction patterns performed, in powder and pellet samples, we have estimated the Lotgering factor along the (00l) direction, F_(00l). The results indicate that F_(00l) increases ~23% with increasing UCP suggesting that grains of these samples are preferentially aligned along the c-axis, which is parallel to the compacting direction. The resistive transition of the samples have been interpreted in terms of the thermally activated flux-creep model. In addition, the effective intergranular pinning energy, U₀, have been determined for different applied magnetic field. The magnetic field dependence of U₀, for B_a > 8 mT, was found to follow a H^{- α} dependence with α = 0.5 for all samples. The analysis of the experimental data strongly suggested that increasing UCP results in appreciable changes in both the grain alignment and the grain connectivity of the samples. We have successfully interpreted the data by considering the existence of three different superconducting levels within the samples: the superconducting grains, the weak-links, and the superconducting clusters.