Effect of Mg doping in enhancing superconductivity in Ni doped (Cu_(0.5)Tl_(0.25)Li_(0.25))Ba_2Ca_(2-y)Mg_y (Cu_(1.5)Ni_(1.5))O_(10-delta) (y = 0, 0.5, 1.0, 1.5) superconductors

摘要

In our recent research findings with Ni doping in Cu_(1-x)Tl_xBa_2Ca_2Cu_(3-y)Ni_yO_(10-delta) (y = 0, 0.5, 1.0, 1.5) superconductors we have not observed any substantial depression of superconductivity. We have substituted Mg at Ca site in Cu_(1-x)Tl_xBa_2Ca_(2_y)Mg_yCu_(1.5)Ni_(1.5)O_(10-delta) (y = 0, 0.5, 1.0, 1.5) superconductors in order to see the effect of enhanced interactions between the Ni~(+2) ions and the mobile carriers in the planes. We have also modified the density of free carriers in conducting CuO_2/NiO_2 planes by the substitution of Li in the charge reservoir layer and also by the self doping (self doping is induced by post-annealing). We have observed from these studies that the c-axis length is increased with Mg doping. The T_c (R = 0) and the magnitude of diamagnetism are improved with Mg doping in Cu_(1-x)Tl_xBa_2Ca_(2_y)Cu_(1.5)Ni_(1.5)O_(10-delta) superconductors. These parameters (the critical temperature and magnitude of diamagnetism) are further enhanced by Li doping in the (Cu_(0.5)Tl_(0.5))Ba_2O_(4-delta) charge reservoir layer and by post-annealing the samples in oxygen atmosphere. The FTIR absorption measurements have shown a hardening of apical oxygen mode around 485 to 497 cm~(-1) with the increased concentration of Mg. These modes are softened in both Mg free and Mg doped samples with the doping of Li, which is most likely arising due to optimized carrier concentration in conducting CuO_2/NiO_2 planes.