Weak link behavior of Sn doped (Cu_(0.5)Tl_(0.5))Ba_2Ca_2(Cu_(3-x)Sn_x)O_(10-delta) superconductors

摘要

(Cu_(0.5)Tl_(0.5))Ba_2Ca_2(Cu_(3-x)Sn_x)O_(10-delta)(x=0,0.25, 0.5,0.75,1.0,1.25,1.5) superconductor samples have been synthesized using solid state reaction method and studied their weak link behavior by carrying out infield ac-susceptibility measurements. These samples have shown a systematic decrease of zero resistivity critical temperature [T_c(R = 0)] with increase Sn doping. The onset of diamagnetism is shifted to lower temperature values and the magnitude of diamagnetism is suppressed. The suppression of magnitude of diamagnetism may possibly be due to increased localization of mobile carriers at Sn~(4+) atoms in SnO_2/CuO_2 planes. The J_c of the samples calculated by using Bean's critical field model have been found to suppress with enhanced Sn doping. The J_c values so obtained are fitted to the power law behavior of the type (1 - T_p/T_c)~n of various values of n. A best fit of n = 1 appropriate for the superconductor insulator superconductor junction (SIS) is achieved both for as-prepared and oxygen annealed samples. The insulating material formed at the grain boundaries is due to oxygen diffusion which possibly provides large surface areas to the shielding currents and enhances the J_c of the final compound.