Intergranular critical currents and excess conductivity in the Fe-substituted Bi-2223 high Tc superconductor

In this paper me present the effect of iron substitution in the (Bi_1.6Pb_0,4)(Sr_1.88Ba_0.2)Ca₂(Cu_1–xFe_x)_3.1O_y system. From the resistivity and AC susceptibility data we observed that a monotonie decrease of T_c occurs with increasing Fe concentration. A strong reduction of J_c (calculated from AC susceptibility data performed at low magnetic fields in the range 0.4A/m-800A/m) is observed in the doped samples. The crossover temperature from the Anderson-Kim thermally activated flux creep to the thermally activated phase slippage behaviour is depending on the doping concentration. The excess conductivity and 2D-3D crossover is well described by considering /₀ as a product of a Gaussian centered at T_c with a Student distribution centered at 2T_c. The alteration of 2D dimensionality above T_c by doping results in the decrease of the number of freedom degrees of the Student distribution.