Abstract
Ce substituted Tl0.9Bi0.1Sr2−xCexCa0.9Y0.1Cu1.99Fe0.01O7−δ (x=0–0.20) samples were synthesized to determine the effects of the higher valence ion substitution on superconductivity and structure of the Fe-doped Tl1212 derivatives. The normal state behavior for x=0 showed semiconductor-like behavior which gradually turned to metallic behavior with increasing Ce at x=0.05–0.15. However, further substitution of Ce for x>0.15 turned the normal state to insulating behavior. The zero critical temperature, Tc zero increased from 65.4 K (x=0.05) to 71.0 K (x=0.10), but slightly decreased for x>0.10 indicating the optimum value of average copper valence was achieved at x=0.10. Excess conductivity analysis using the Aslamazov Larkin, AL and Lawrence–Doniach, LD models revealed two-dimensional, 2D to three-dimensional, 3D transition of superconducting fluctuation behavior, SFB with the highest transition temperature, \(T_{\mathrm{2D}\mbox{-}\mathrm{3D}}\) at x=0.10. FTIR analysis in conjunction with XRD results showed softening of FeO2/CuO2 planar oxygen mode from 610.5 cm−1(x=0) to 605 cm−1(x=0.20) which is suggested to be related to possible increase of inter plane coupling, J and this is supported by computed results based on the LD model. The enhanced J increases superconducting coherence length along c-axis, ξc(0), and hence lowers anisotropy, γ resulting in enhanced superconducting properties.
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