Synthesis and excess conductivity analysis of TlBa2(Ca3−y Be y )Cu4O12−δ superconductors

Abstract

TlBa2(Ca3−yBey)Cu4O12−δ (y = 0, 0.5, 1.0, 1.5, 2) samples are synthesized at normal pressure and the influence of doped Be-atoms on the superconductivity parameters at the microscopic level is investigated by carrying out excess conductivity analyses of conductivity data. The samples have shown tetragonal structure and the unit cell volume decreases with increased Be-doping. The onset temperature of superconductivity [Tc(onset)] and zero resistivity critical temperature [Tc(R = 0)] decrease with increased Be, however, the magnitude of diamagnetism is enhanced with Be (except for Be-doping of y = 1.0). The apical oxygen mode of the type Tl–OA–Cu(2) and CuO2 planar oxygen mode are softened as observed in FTIR absorption measurements. The FIC analyses of conductivity data have shown an increase in the coherence length along the c-axis and inter-plane coupling. The values of Bc0(T), Bc1(T), Jc(0), τφ are improved with the doping of Be. These observations suggested that due to the proximity effect there is less suppression in the value of the order parameter of the Cooper pairs from |ψ|2 = 1 value in the CuO2 planes in Be-doped samples that maintains the density of carriers in the conducting CuO2 planes [since the |ψ|2 = n/2] which promotes enhancement in the magnitude of superconductivity.