Normal-state properties of uniaxially pressed Bi1.65Pb0.35Sr2Ca2Cu3O10+δ ceramics

We have studied the effects of the uniaxial compacting pressure on the physical properties of polycrystalline Bi1.65Pb0.35Sr2Ca2Cu3O10+delta (Bi-2223) superconductors. Powders of this material were pressed at different uniaxial compacting pressures ranging from similar to 90 to similar to 600 MPa and heat-treated at the same temperature. A characterization of samples by using Scanning Electron Microscopy and X-ray diffractometry indicated an appreciable improvement of the degree of texture with increasing pressure. The temperature dependence of the electrical resistivity p(T) exhibits a T-linear behavior at temperatures higher than T* - 235 K. The deviation of p(T) from the linear behavior below T* indicates the opening of the pseudogap, a feature confirmed by magnetic susceptibility measurements performed in powder samples. From linear fittings of the normal-state electrical resistivity we were able to separate contributions to p(T) arising from both the grain misalignment and microstructural defects. The results suggest that the grain orientation and the connectivity between them are improved with increasing compacting pressure. Also, based on the linearity of the electrical resistivity data both the transport electron-phonon coupling constant, a., and the mean free path, l, were estimated. We have found that in the sample with the highest degree of texture lambda(tr) similar to 0.53, a value comparable with the one obtained in Bi-2223 single crystals. However, the result for l similar to 12.7 angstrom at 300 K, in the same ceramic sample, is close to 3 times lower than the single crystal value. The influence of the intergranular electrical resistivity in determining band-theory parameters was analyzed within the framework of a current conduction model for granular superconducting materials.