AC Susceptibility and Excess Conductivity Analysis of Cd Substituted (Tl0.6Bi0.4)Sr2(Ca1-x Cdx)Cu2O7-δ Superconductor

Abstract

The effect of Cd on (Tl 0.6 Bi 0.4 )Sr 2 (Ca 1-x Cd x )Cu 2 O 7-δ (Tl-1212) superconductor is reported. Cd was chosen to partially replace Ca due to the single valence (+2) of both elements and this work is focused on the ionic radius effect on this phase. The solid-state reaction route was utilized to prepare (Tl 0.6 Bi 0.4 )Sr 2 (Ca 1-x Cd x )Cu 2 O 7-δ (Tl-1212) with x = 0 to 0.20. Tl-1212 was dominant as indicated by xray diffraction patterns. The x = 0.15 sample showed the highest onset temperature T c-onset (95 K). The peak temperature, T p of χ" (imaginary part of the AC susceptibility) decreased pronouncedly with Cd content indicating weakening of inter-grain coupling. Cd substitution reduced the 2-dimensional to 3dimensional conductivity transition from 139 K (x = 0) to 135 K (x = 0.15). From Lawrence-Doniach model it was shown that the sample with the highest T c-onset (x = 0.15) exhibited the shortest coherence length, highest anisotropy (γ = 9.692 ) and weakest inter-layer coupling (J = 0.421). Cd substitution lowers both the inter-layer and inter-grain coupling. These factors are important in optimizing the superconductivity of the Tl-1212 phase.