Charge Transfer Mechanism and Superconductivity in Tl0.5Cu0.5 (Ba1−x Sr x )Ca2Cu3O y (x = 0, 0.15,0.25,0.35) Samples

Abstract

Tl0.5Cu0.5(Ba1−x Sr x )Ca2Cu3O y (x = 0, 0.15,0.25,0.35) superconductors are prepared by a two-step solid-state reaction method, and their superconducting properties are studied by resistivity, susceptibility, FTIR, XRD, and excess conductivity analyses. The samples have shown an orthorhombic crystal structure in which the c-axis length and the volume of the unit cell increase with Sr doping. The normal-state resistivity is appreciably suppressed, and the zero resistivity critical temperature observed between 97 and 104 K. The magnitude of the superconductivity is enhanced in Sr-doped samples. In the Fourier transform infrared (FTIR) absorption measurements, the apical oxygen phonon mode is observed to be softened with Sr doping whereas the peak position of planar oxygen stays unaltered in Sr-incorporated samples. The excess conductivity analyses of Tl0.5Cu0.5(Ba1−x Sr x )Ca2Cu3O y (x = 0, 0.15,0.25,0.35) samples have shown that the values of ξ c(0), the inter-layer coupling J, are not appreciably altered whereas the Fermi velocity v F of superconducting carriers and the phase relaxation increase with Sr doping. The values of parameters such as B c0(T), B c1(T), J c(0) are, however, enhanced with the doping of Sr in the final compound. These studies have shown that Sr doping promotes efficient transfer of the carriers from charge reservoir layer to the conducting CuO2 planes thereby promoting enhancement in the density of carriers and hence increase in the values of aforementioned superconductivity parameters.