Superconducting fluctuation and infrared absorption of Cd-substituted Tl0.9Bi0.1Sr1.8Yb0.2Ca1−xCdxCu1.99Fe0.01O7−δ ceramics

Tl0.9Bi0.1Sr1.8Yb0.2Ca1−xCdxCu1.99Fe0.01O7−δ (x=0–0.4) ceramics were prepared using the conventional solid-state synthesis method to investigate the effects of Cd2+ substitutions on superconducting fluctuation behavior, SFB and structural properties of the Tl1212 derivatives. Electrical resistivity measurements showed all the samples exhibit metallic normal-state behavior with zero resistivity critical temperature, Tc zero increasing from 40.0 K (x=0) to 76.4 K (x=0.3) before decreasing to 74.8 K (x=0.4) with increasing Cd2+. FTIR analysis in conjunction with XRD results indicates improved inter-plane coupling that is evidenced in the form of decreased c-axis length and softening of the apical oxygen mode when Cd concentration was increased. In order to study the effect of Cd substitutions on SFB, excess conductivity analysis above Tc was performed using the Aslamazov–Larkin, AL model in conjunction with the Lawrence–Doniach, LD model. The results showed cross-over between two-dimensional, 2D to three-dimensional, 3D SFB transition for all the samples (x=0.1–0.4) with decreasing temperature. The highest transition temperature, T2D–3D was observed at x=0.3 which showed both the longest coherence length, ξc(0) and the highest inter-plane coupling constant, J within the series. Our results suggest that the increase in J and lowering of anisotropy, γ resulted in enhancement of superconductivity in the compound.