CURRENT-VOLTAGE CHARACTERISTICS AND TRANSPORT CURRENT DISTRIBUTIONS IN AG BI-2223 MONOCORE TAPES/

Current-voltage characteristics of Ag-sheathed Bi-2223 monocore tapes have been measured at 77 K in low d.c. magnetic fields. Results have b een obtained with the c-axis of the sample both parallel and perpendic ular to the applied field, together with the force-free orientation. T he current-voltage characteristics have been analysed in terms of thei r n-value (VocI(n)), which characterizes the sharpness of the resistiv e transition and the second differential (d(2)V/dI(2)) which shows the distribution in local critical current density values. The second dif ferential has been fit;ed and analysed using the phenomenological Weib ull distribution function, which is based on a weak-link model. The fo ur parameters of this function have been used to investigate the micro structural nature of the sample, in particular, the factors influencin g the critical current density and the transport current pathways. The results are consistent with the view that at low fields the critical current density is limited by weak-link grain boundaries and at high f ields by intra-granular flux pinning. (C) 1998 Elsevier Science Ltd. A ll rights reserved.