INTERGRANULAR CRITICAL CURRENTS AND EXCESS CONDUCTIVITY IN THE FE-SUBSTITUTED BI-2223 HIGH-TC SUPERCONDUCTOR

In this paper we present the effect of iron substitution in the (Bi1.6 Pb0.4)(Sr(1.88)Bu(0.2))Ca-2(Cu1-xFex)(3.1) O-y system. From the resist ivity and AC susceptibility data we observed that a monotonic decrease of T-c occurs with increasing Fe concentration. A strong reduction of J(c) (calculated from AC susceptibility data performed at low magneti c fields in the range 0.4A/m-800A/m) is observed in the doped samples. The crossover temperature from the Anderson-Kin thermally activated f lux creep to the thermally activated phase slippage behaviour is depen ding on the doping concentration. The excess conductivity and 2D-3D cr ossover is well described by considering Delta sigma/sigma(0) as a pro duct of a Gaussian centered at T-c with a Student distribution centere d at 2T(c). The alteration of 2D dimensionality above T-c by doping re sults in the decrease of the number of freedom degrees of the Student distribution.