Transport and ac susceptibility measurements on silver wrapped pellets of Bi_1.7Pb_0.35Sr_1.9Ca_2.1Cu₃O_y superconductors

The effect of the cooling rates on oxygen content of silver sheathed Bi-2223 bulk superconducting samples was investigated performing dc electrical resistivity, transport critical current density, ac susceptibility and x-ray diffraction (XRD) measurements. The bulk samples with Ag sheathing were annealed under identical conditions and cooled with rates of 25° C / h, 50° C / h, 75° C / h, and 100° C / h. We estimated the transition temperatures from both dc resistivity and ac susceptibility as a function of temperature measurements. It is observed that T_c and J_c depend on cooling rates of the samples. T_c and J_c decrease with increasing cooling rates. The imaginary part of ac susceptibility measurements is used to calculate inter-granular critical current density using the Bean Model. J_c(T_p) is also seen to decreases with increasing cooling rates. The peak temperature, T_p, in the imaginary part of the ac susceptibility is shifted to a lower temperature with increasing cooling rates as well as increasing ac magnetic fields. The force pinning density decreased with increasing the cooling rates. XRD patterns are given to determine lattice parameter c and obtain information about Bi-2223 and Bi-2212 phases.