Investigación

 

Fluctuation-induced conductivity of polycrystalline Gd_1-χCe_χBa₂Cu₃O_7-δ superconductor

 

M. Murerª, Y. Aparecido Opataª, J.F.H. Leandro Monteiroª, S. Aparecida da Silvaª, P. Rodrigues Júniorª and A.R. Jurelo^b

 

ª Departamento de Física, Universidade Estadual de Ponta Grossa, Av. Gen. Carlos Cavalcanti 4748, 84.030-000, Ponta Grossa, Paraná, Brazil.

^b Departamento de Física, Universidade Estadual de Ponta Grossa, Av. Gen. Carlos Cavalcanti n° 4748, 84.030-000 Ponta Grossa, Paraná, Brazil, Tel: +55 42 3220 3044; Fax: +55 42 3220 3042, e-mail: arjurelo@uepg.br

 

Recibido el 2 de mayo de 2012;
Aceptado el 15 de junio de 2012

 

Abstract

This paper reports on measurements of the resistive transition in polycrystalline Gd_1-χ Ce_χ Ba₂ Cu₃ O_7-δ samples (x = 0.000, 0.025 and 0.050). The samples were produced by a standard solid state reaction method and in two different thermal routes. The microstructure was analyzed by X-ray diffraction. The samples were considered homogeneous since no extra peaks due to impurity phase were observed. To identify power-law divergences in conductivity, the results were analyzed in terms of the temperature derivative of the resistivity and the logarithmic temperature derivative of the conductivity (d ln (Δσ) /dT). From the results, the occurrence of a two-stage transition besides the pairing transition splitting for sample with x = 0.050 was observed. Such splitting was associated with Ce doping and related with the occurrence of a phase separation. In the normal phase, Gaussian and critical fluctuations conductivity regimes were identified. Ón approaching the zero resistance state, our results showed a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array.

Keywords: High-T_C superconductor; polycrystalline; gadolinium; cerium; critical phenomena; fluctuation effects.

 

PACS: 74.40.+k; 74.81.Bd; 74.72.-h

 

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Acknowledgements

This work was partially financed by the CNPq Brazilian Agency under contract n⁰ 474077/2007-1.

 

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