Structure and superconducting properties of Fe-doped Cu0.5Tl0.5Ba2Ca2Cu3-yFeyO10-δ (y=0, 0.02, 0.03, 0.05, 0.075) superconductor

The effects of Fe-doping on superconductivity and structure of Cu0.5Tl0.5Ba2Ca2Cu3-yFeyO10-delta (y = 0, 0.02, 0.03, 0.05, 0.075) superconductors are investigated by means of resistivity, AC-susceptibility measurements, X-ray diffraction (XRD) and thermogravimetric analysis. The X-ray data indicates that the lattice parameters a and c vary but structure of the samples remain tetragonal with predominant CuTl-1223 phase. The c-axis length observed by X-ray diffraction analysis has been found to decrease with the increased Fe-doping content in the unit cell. The thermogravimetric analysis shows that Fe3+ ions replacing for Cu2+ ions can bring excess oxygen atoms into lattice and form some Fe-O defect clusters. In the doping level of Fe (y = 0-0.075), both zero-resistance temperature T-c (R = 0) and the magnitude of diamagnetic signal decrease linearly with the increasing amount of Fe. The striking linear depression of T (R = 0) and the magnitude of diamagnetism suggest the potential effects of charge localization on the transport properties and also shows that Fe dopants occupy different Cu sites in a stable manner with Fe content increasing. The post-annealing experiments demonstrated that the magnitude of diamagnetism as well as T-c (R = 0) is enhanced. It may be due to the delocalization of carriers which result into the enhancement of the density of mobile carriers in the conducting CuO2 planes. Our discussion suggests that the micro structural distortion and the excess oxygen defect induced by Fe-doping encourage in the localization of mobile carriers in conducting CuO2 planes, which is one of the reasons to explain the decrease of T-c (R = 0) and carrier concentration. (C) 2008 Elsevier B. V. All rights reserved.