Fluctuation-induced conductivity of five planar Cu0.5Tl0.5Ba2Ca4−xMgxCu5O14−δ (x = 1, 2) superconductors

Excess conductivities of polycrystalline, as-prepared and oxygen post annealed Mg doped samples have been studied from the resistivity versus temperature data. The logarithmic plots of excess conductivity versus reduced temperatures [(T-Tcmf)/Tcmf] show two cross-over temperatures with three exponents. Except for the as-prepared sample with x = 1 all the samples have shown a distinct cross-over from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov–Larkin equations. Interlayer-coupling strength estimated by using Lawrence–Doniach equations has been observed to increase with higher Mg doping and post-annealing. The improved properties with the higher Mg concentration might be arising from the reduction of the anisotropy along the c-axis. The oxygen post-annealing seems to improve carrier concentration in the conducting CuO2 planes that may be responsible for 2D–3D cross-over of the excess conductivity.