Enhancement of superconductivity of TlBa2Ca3Cu4O12−δ superconductors by Be doping

Abstract

A reproducible synthesis and characterization of the TlBa2(Ca3−yMy)Cu4O12−δ (M=0, Be; y=0, 0. 5, 1.0, 1. 5, 2) superconductors have been studied by using x-ray diffraction, resistivity, ac-susceptibility and FTIR absorption measurements. The x-ray diffraction (XRD) studies of these samples have shown a tetragonal structure in which the length of cell parameters and volume of the unit cell have been found to decrease with increased Be-doping. The zero resisitivity critical temperature [Tc(R=0)] have been suppressed with Be doping. A significant increase in the onset temperature of superconductivity have been observed in Be doped O2 annealed samples. The magnitude of diamagnetism of as prepared samples is higher for particular level of doping. In comparison with as-prepared samples, an improvement in the magnitude of diamagnetism could be witnessed in all oxygen post-annealed samples. It is most likely that oxygen optimization in the unit cell which promotes increase the superconducting properties of TlBa2(Ca3-yBey)Cu4O12−δ (y=0, 0.5, 1.0, 1.5, 2) samples in terms of increased magnitude of diamagnetism. The softening of apical oxygen mode of the type Tl-OA-Cu(2) and CuO2 planar oxygen mode have been observed providing unequivocal evidence of the enhanced inter-plane coupling. In comparison with Be as-prepared samples, the magnitude of diamagnetism is significantly suppressed in O2 annealed samples. It is most likely that oxygen optimization in the unit cell suppresses the density of the carriers and hence the superconducting properties of the final compounds. The doped Be atoms suppress the density of anti-ferromagnetic aligned moments existing in the inner CuO2 planes of TlBa2(Ca3−yMy)Cu4O12−δ [M=Be] which enhance the magnitude of superconductivity in the final compound.