P. Muné

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

We have studied the effects of the uniaxial compacting pressure on the physical properties of polycrystalline Bi1.65Pb0.35Sr2Ca2Cu3O10+d (Bi-2223) superconductors. Powders of this material were pressed at different uniaxial compacting pressures ranging from ~ 90 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 r(T) exhibits a T-linear behavior at temperatures higher than T* ~ 235 K. The deviation of r(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 r(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, ltr, and the mean free path, l, were estimated. We have found that in the sample with the highest degree of textureltr ~ 0.53, a value comparable with the one obtained in Bi-2223 single crystals. However, the result for l ~ 12.7 A 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.

Intragranular defects and Abrikosov-Josephson vortices in Bi-2223 bulk superconductors

The Abrikosov–Josephson (AJ) vortices that emerge at intragranular defects of Bi-2223 bulk superconductors are detected. The study is based on the combination of magnetic and transport characterizations with a brief theoretical formulation that allow estimating the minimum angle of the intragranular planar defects where the AJ vortices emerges for a given applied magnetic field. Measurements of magnetization versus applied magnetic field,

Electrical effective parameters of the grains and the Montgomery's method in \(\hbox {Bi}_{1.65}\hbox {Pb}_{0.35}\hbox {Sr}_2\hbox {Ca}_{2.5}\hbox {Cu}_{3.5}\hbox {O}_y\) ceramics

M(H_{a})

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

M(Ha), in powder samples reveal that the intrinsic anisotropy effects of the grains in these materials suffer almost a complete attenuation due to their high shape anisotropy. In fact, powder samples behave as composed of isotropic grains with lower critical field ~80 Oe. However, a more detailed analysis of the quasi-linear part of these curves show that the penetration of the magnetic flux into intragranular defects occurs at similar values of applied magnetic fields than those reported in whiskers or well textured ceramics for their two main perpendicular directions which are lower values than ~80 Oe. Finally, taking into account a brief theoretical formulation, we have found that in the case of defects where the magnetic flux penetrates perpendicular to the c-axis of the crystallites (~30 Oe) approximately the stacking faults and defects with misorientation angles higher than ~14

Microstructural properties of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ and Bi1.65Pb0.35Sr2CaCu2O8+δ ceramic samples through transport measurements: a comparative study

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Penetration and trapping of the magnetic flux in planar defects of Bi1.65Pb0.35Sr2Ca2+xCu3+xOy superconductors

∘ can be the main causes of flux-trapping, but the mechanism may change to low misorientation angles defects, less than ~6