Superconducting Fluctuations and Excess Conductivity Analysis of Te-Substituted TlSr2(Ca1−x Te x )Cu2O7−δ
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Samples with nominal starting compositions TlSr2(Ca1−x Te x )Cu2O7−δ (x = 0.05–0.30) were prepared by the solid-state reaction method and studied by powder X-ray diffraction and electrical resistance measurements. The purpose of this work was to determine the valence state of Te in the TlSr2CaCu2O7−δ (Tl-1212) phase. It is also to determine the dimension of fluctuation-induced conductivity λ, and the superconducting fluctuations and excess conductivity using the Aslamazov–Larkin (AL) theory. The Lawrence–Donaich (LD) theory was used to calculate the coherence length ξ c(0), interlayer coupling J, and anisotropy γ = (ξ ab(0)/ ξ c(0)). X-ray powder diffraction patterns indicated that the samples were dominantly Tl-1212 phase. Temperature-dependent resistance measurements showed metallic normal-state behavior for all samples. The onset transition temperature, T c onset, was between 32 K (x = 0.05) and 61 K (x = 0.25). The valence of Te in Tl-1212 is suggested to be Te6+ from the analysis of the highest T c in the x = 0.25 sample. Excess conductivity analyses showed that Te substitution induced 2D-to-3D conductivity transition with the highest transition temperature, T 2D−3D observed for x = 0.25. The calculations based on Lawrence–Doniach model showed the shortest coherence length, ξ c(0), and highest anisotropy (γ = 10.24) for the x = 0.25 sample.
KeywordsTl-1212 Solid-state reaction Excess conductivity
This work has been supported by the Ministry of Education of Malaysia under grant no. FRGS/2/2013/SG02/UKM/01/1 and Universiti Kebangsaan Malaysia under grant no UKM-DIP-2014-022.