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Superconductivity at 9.5 K in the Ti2GeC compound

Bortolozo A. D., Sant'Anna O. H., Dos Santos C. A. M., Machado A. J. S.

Materials Science Poland

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2012

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Vol. 30, No. 2

92--97

EN

We report on the investigation of the Ti2GeC properties by X-ray diffraction, magnetic and electrical resistivity measurements. Polycrystalline samples of Ti2GeC with nominal compositions were prepared by solid state reaction. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr2AlC prototype. The temperature dependence of both electrical resistivity and magnetization indicate a bulk type-II superconductivity at 9.5 K. Magnetoresistive data suggest an upper critical field of Bc2 -- 8.1 T and coherence length - 61 A° . Furthermore, the results highlight the highest critical temperature reported up to now for an H-phase.

2

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

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2010

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Vol. 28, No. 3

639--645

EN

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.

3

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

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2009

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Vol. 27, No. 2

569--579

EN

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.