Study of the intergranular coupling of Cu_(0.5)Tl_(0.5)Ba_2Ca_(2-y)Mg_yCu_3O_(10-delta)(y = 0, 0.5,1.0 and 1.5) superconductors

摘要

The intergranular properties of Cu_(0.5)Tl_(0.5)Ba_2Ca_(2-y)Mg_yCu_3O_(10-delta) superconductor have been studied by resistivity and AC magnetic susceptibility measurements. Magnesium substitution has been found to improve the interplane coupling in the unit cell of Cu_(0.5)Tl_(0.5)Ba_2Ca_(2-y)Mg_yCu_3O_(10-delta), which in turn would enhance the intergranular coupling. The main objective of the present studies was to observe any possible role played by Mg doping in developing and enhancing the intergranular coupling and flux pinning properties of this compound. Any improvement to the intergrain coupling may be promoted by a change in the oxygen content in the final compound. Since the loss and/or intake of oxygen occurs at T_a > = 350 deg C, the post-annealing experiments were carried out at 500 deg C for 3 h in air, nitrogen and oxygen atmospheres. It was observed from these studies that the oxygen contents decreased in all the samples after post-annealing in air, nitrogen and oxygen atmospheres. The most prominent effects in terms of enhanced superconductivity in the intergranular regions are observed in Mg-doped samples after post-annealing in air. The Mg-doped samples have shown enhanced granular connectivity, since the intergranular coupling peak observed in chi'' in AC susceptibility measurements is shifted to higher temperatures with the increase of Mg concentration. The enhanced intergranular coupling and flux pinning in magnesium-substituted samples is also observed in AC susceptibility measurements in external magnetic fields. The enhancement of intergranular coupling increases the transport critical current density of the samples.