Influence of Ce Substitution at Sr-Site on Superconducting Fluctuation Behavior and Infrared Absorption of Tl_(0.9)Bi_(0.1)Sr_(2-x)Ce_xCa_(0.9)Y_(0.1)Cu_(1.99)Fe_(0.01)O_(7-δ) (x = 0-0.20) Ceramics

摘要

Ce substituted Tl_(0.9)Bi_(0.1)Sr_(2-x)Ce_xCa_(0.9)Y_(0.1) Cu_(1.99)Fe_(0.01)O_(7-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, T_(c 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_(2D-3D) at x = 0.10. FTIR analysis in conjunction with XRD results showed softening of FeO_2/CuO_2 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, ξ_c(0), and hence lowers anisotropy, γ resulting in enhanced superconducting properties.