Superconducting properties of Cd doped Cu0.5Tl0.5Ba2Ca3Cu4-yCdyO12-δ (y = 0, 0.25, 0.5, 0.75, 1.0) superconductors

Cadmium doped Cu0.5Tl0.5Ba2Ca3Cu4-yCdyO12-δ (y = 0, 0.25, 0.5, 0.75, 1.0) samples have been synthesized and their superconducting properties are studied using X-ray diffraction (XRD), resistivity, ac-susceptibility and Fourier Transform Infrared (FTIR) absorption measurements. These samples have shown tetragonal structure, their unit cell volume is decreased with the increased Cd doping. The zero resistivity critical temperature [Tc(R = 0)] decreases and the magnitude of diamagnetism is suppressed with the increased concentration of Cd in superconductors. The Tc(R = 0) and the magnitude of diamagnetism in these compounds are improved after post-annealing in oxygen atmosphere. It is most likely that the increased concentration of oxygen in Cu0.5Tl0.5Ba2O4-δ charge reservoir layer optimizes the density of carriers in the conducting planes to the desired level consequently increasing superconductivity in the final compound. Changes in the shape of FTIR absorption spectra after Cd doping have shown incorporation of Cd in the unit cell of the final compounds. The FTIR absorption measurements of these samples have shown hardening of apical oxygen modes of type Cu(1)-OA-Cu(2)/Cdy (y = 0, 0.25, 0.5, 0.75, 1.0) with increased Cd doping. It is most likely that hardening of apical oxygen modes of vibration are associated with the damped harmonic oscillations of heavier Cd atoms in the CuO2 planes which suppress the phonons population from a desired level reducing the magnitude of superconductivity in the final compound.