The reduced weak links in Cu 0.5Tl 0.5Ba 2Ca 4− xMg xCu 5O 14− δ ( x = 1, 2 and 3) superconductors

Abstract

The weak links in Cu 0.5Tl 0.5Ba 2Ca 4− x Mg x Cu 5O 14− δ ( x = 1, 2 and 3) superconductors have been reduced by carrying out post-annealing of samples in the air, oxygen and nitrogen atmospheres. The weak link behavior is studied from the width and peak temperature ( T P) of out of phase component of magnetic susceptibility ( χ″). A broad χ″ magnetic transition associated with a lower T P a finger print of the weak links in oxide superconductors, was observed in the as-prepared samples. After post-annealing the samples in the air, oxygen and nitrogen atmospheres this transition is changed to a sharp χ″ peak and the T P is shifted to higher temperatures; which is an evidence of strong intergrain coupling. These effects are most prominently observed in oxygen post-annealed samples. The post-annealing in oxygen possibly promotes oxygen intake to the intergrain sites resulting into oxides of respective elements appearing at the termination ends of the crystals, i.e. grain boundaries. The formation of these oxides at the grain boundaries possibly provides large surface area to the shielding currents, better intergrain coupling, a sharp out of phase component of magnetic susceptibility ( χ″) and higher quantity of diamagnetism.