The (Cu0.5Tl0.5)Ba2O4−δ charge reservoir layer as an efficient source of carriers to the CuO2 planes: Doping of Bi in (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors

In order to study the higher carrier's doping efficiency of (Cu0.5Tl0.5)Ba2O4−δ charge reservoir layer to the conducting CuO2 planes we have incorporated Bi in (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors; the presence of Bi in the charge reservoir layer promotes highest anisotropy to these compounds. For such studies, we have successfully synthesized (Cu0.25Tl0.5Bi0.25)Ba2Ca2Cu3O10−δ, (Bi0.5Tl0.5)Ba2Ca2Cu3O10−δ, (Cu0.25Tl0.25Bi0.25Li0.25)Ba2Ca2Cu3O10−δ and (Cu0.25Tl0.25Bi0.25Li0.25)Ba2Ca2−yBeyCu3O10−δ superconductors at normal pressure and studied their superconducting properties. These studies have shown that incorporation of Bi at the charge reservoir layer promoted a decrease in the density of carriers in the conducting CuO2 planes which in turn suppressed the magnitude of diamagnetism of final compound. The decreased density of the carriers in the CuO2 planes, which most likely promotes inferior superconducting properties, was replenished by doping of Li in the charge reservoir layer and optimizing their number by post-annealing in oxygen atmosphere. It is observed that Bi doping in (Cu0.5Tl0.5)Ba2O4−δ charge reservoir layer promotes an increase in the c-axis length which in turn increase the anisotropy and decrease the Fermi-vector [kF = (3π2 N/V)1/3] and Fermi-velocity [vF=(πεcΔ/ℏ)] of the carriers. We have decreased the c-axis length of Bi doped compounds by doping Be at the Ca sites in (Cu0.25Tl0.25Bi0.25Li0.25)Ba2Ca2−yBeyCu3O10−δ superconductors. It is observed from these experiments that Beryllium doping of y = 0.5 has produced excellent superconducting properties in terms of enhancement of Tc(R = 0) and magnitude of diamagnetism in this compound. A maximum decrease in the unit cell volume is observed with this Be doping concentration, which enhance kF, vF and superconducting order parameter of the carriers and hence promote the enhancement of superconducting properties. These studies have also shown that the role of density of the carriers in CuO2 planes is pivotal in the mechanism of superconductivity in these compounds and Bi doping significantly affects them due to its presence in the charge reservoir layer.