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Structural characterization and electrical resistance of the BaPb1-xBixO3 system

Da Luz M. S., Coelho A. D. A., Dos Santos C. A. M., Izario Filho H. J., Machado A. J. S.

Materials Science Poland

2010

Vol. 28, No. 3

639--645

The electrical resistance R(T) in function of temperature T, and X-ray powder diffraction (XRD) patterns of polycrystalline samples of the BaPb1-xBixO3 system have been described. R(T) measurements of single phase samples show that BaPbO3 exhibits metal-like properties, and that the system exhibits super-conductivity in the 0.005 < x < 0.30 range, but insulating properties for x > 0.30. A careful analysis of the onset of the critical temperature (TC) reveals its strong dependence on the sample composition in the range 0.005 < x < 0.30 which may be related to the superconducting volume fraction ultimately leading to connected or disconnected superconducting clusters, similar to those observed in granular superconductors.

The van der Pauw method of measurements in high-Tc superconductors

Da Luz M. S., Dos Santos C. A. M., Shigue C. Y., De Carvalho Jr. F. J. H., Machado A. J. S.

Materials Science Poland

2009

Vol. 27, No. 2

569--579

Details on the transport measurements of high-Tc superconductors have been presented using the van der Pauw technique. Basic procedures to obtain good and reliable results in polycrystalline samples were discussed. The influence of heating rates and the direction of the applied magnetic field on the results of measurements has been examined. An unexpected nonzero transverse voltage at zero magnetic field was observed in the vicinity of the superconducting temperature transition (Tc). Measurements in two different magnetic field directions allowed one to calculate the symmetric and the asymmetric components of the Hall resistance. Those components were calculated for two different superconductor systems and analyzed in the framework of the recent theory about the longitudinal and transverse voltages in high-Tc superconductors.