Superconducting properties of Ni-substituted CuTl-1223 superconductor

Superconducting properties of Cu0.5Tl0.5Ba2Ca2(Cu3-xNix)O10-delta (x = 0, 0.5, 1, 1.5) have been investigated by XRD, dielectric measurements, excess conductivity analyses and resistivity measurements. These samples show orthorhombic crystal structure in which a-axis length suppresses but b-axis length increases with increased Ni concentration. These samples have shown metallic variations of resistivity from room temperature down to onset of superconductivity in which the onset temperature of superconductivity and its zero resistivity critical temperature suppresses with increased Ni concentration. Excess conductivity analyses of conductivity data has shown values of coherence length xi(c(0)) along c-axis, Fermi velocity of the carriers V-F and inter-layer coupling J, suppress with increased Ni-substitution which shows that density of superconducting carriers is also suppressed. Lower values of real part (epsilon ') of dielectric constant has confirmed lower density of carriers in Ni-doped samples which further shows that doped Ni-atoms induce pair breaking effects. The flux pinning characteristics of Ni substituted samples are, however, significantly improved in comparison with parent compound i.e. Cu0.5Tl0.5Ba2Ca2Cu3O10-delta, manifesting that spin carrying Ni-atoms behave like efficient pinning centers.