Superconducting Properties of Zn-Doped Cu0.5Tl0.5Ba2Ca2Cu3−y Zn y O10−δ Superconductors

Abstract

A reproducible synthesis and characterization of Zn-doped Cu0.5Tl0.5Ba2Ca2Cu3−yZnyO12−δ (y=0, 0.5, 1.0, 1.5) superconductors at a relatively lower synthesis temperature of 840°C are 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 c-axis length has been found to decrease with increased Zn doping. The critical temperature and magnitude of diamagnetism have not been significantly affected with the doping of Zn at this synthesis temperature. The magnitude of diamagnetism in the as-prepared undoped samples is decreased, whereas it remains stable (unchanged) in oxygen post-annealed samples. The apical oxygen phonon’s modes of type Tl–OA–M(2) and Cu(1)–OA–M(2) {where M=Cu/Zn} and the planar oxygen phonon modes of type M(2)–OP–M(2) are also softened with the increase of Zn doping. We interpreted the softening of these oxygen related phonon modes linked with the decreased c-axis length, reduced John–Teller distortions and increased mass of Zn (65.38 amu) as compared to that of Cu (63.54 amu) (Kaplan et al., Phys. Rev. B 65, 214509, 2002).