Effects of Ce4+ and Cd2+ substitutions on superconducting fluctuation behavior, ultrasonic velocity and elastic properties of Fe- doped (Tl, Bi)-1212 high temperature superconductors / Shabani Ismail

In this study, two series of superconductor compounds with starting composition Tl₀.₉Bi₀.₁Sr₂₋ₓCeₓCa₀.₉Y₀.₁Cu₁.₉₉Fe₀.₀₁O₇₋δ (x = 0–0.20) and Tl₀.₉Bi₀.₁Sr₁.₈Yb₀.₂Ca₁₋ₓCdₓCu₁.₉₉Fe₀.₀₁O₇-δ (x = 0–0.4) ceramics were prepared using the conventional solidstate synthesis method to elucidate their physical properties. For Cesubstituted of Tl₀.₉Bi₀.₁Sr₂₋ₓCeₓCa₀.₉Y₀.₁Cu₁.₉₉Fe₀.₀₁O₇₋δ (x = 0–0.20) samples, 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 threedimensional, 3D transition of superconducting fluctuation behavior, SFB with the highest transition temperature, T2D-3D at x = 0.10. FTIR analysis in conjunction with XRD results showed softening of FeO₂/CuO₂ planar oxygen mode which is suggested to be related to possible increase of interplane coupling, J and this is supported by computed results based on the LD model…