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

• Autor(a) principal: Govea-Alcaide,E.
• Data de Publicação: 2005
• Outros Autores: Muné,P., Jardim,R. F.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Brazilian Journal of Physics
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332005000400016

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 ~ 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 rho(T) exhibits a T-linear behavior at temperatures higher than T<FONT FACE=Symbol>*</FONT> ~ 235 K. The deviation of rho(T) from the linear behavior below T<FONT FACE=Symbol>*</FONT> 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 rho(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, lambdatr, and the mean free path, l, were estimated. We have found that in the sample with the highest degree of texturelambdatr ~ 0.53, a value comparable with the one obtained in Bi-2223 single crystals. However, the result for l ~ 12.7 Å 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.