Experimental assessment of the current-limiting mechanisms in BSCCO/Ag high-temperature superconducting tapes

Abstract

The current-voltage characteristics and the magnetic field dependence of the critical current of a range of mono-core BSCCO 2223 tapes are presented, illustrating the complementary use of transport and magnetization experiments in determining and analysing the current-limiting dissipation processes in these HTS conductors. Below a magnetic cross-over field H * the samples resemble a Josephson-linked current network, with the dominant dissipation at the weakest grain boundaries. In this regime, increasing field leads to a gradual fragmentation of the network. The network homogeneity and connectivity can be inferred from screening current length-scale measurements and comparison of transport and magnetization measurements. Above the cross-over field H * , flux motion within the surviving strongly linked backbone dominates the dissipation. The details of the dependences of the critical current and flux creep rate on magnetic field can be used to examine the intragranular pinning potential in the tapes. We show that, despite the wide range of transport critical-current values of the samples examined, the intragranular pinning proves to be remarkably sample independent. We conclude that while J c at low fields may be increased by improved processing that yields better intergrain connectivity, the high-field J c can be enhanced only by strengthening the pinning within the BSCCO 2223 crystallites themselves.

Comparing powder magnetization and transport critical current of Bi,Pb(2223) tapes

“…The aim of this paper is to verify the validity of the parallel-path assumption through a careful comparison between powder magnetization and the overall dependence of intact tapes. In this respect, it resembles earlier studies on Bi,Pb(2223) tapes [1], but with two key differences. Firstly, whereas the earlier work focused on the high-field behavior, in order to bring out the similarities between the macroscopic critical current and the powder magnetization in this regime, our data are analyzed with special attention to the low-field regime.…”

“…Secondly, the transport data yield a characteristic decay field that is nearly ten times higher than that obtained by magnetization. This can be understood as a consequence of the different electric fields occurring in the experiments [1]. More importantly, the temperature dependence of is nearly the same for transport and magnetization.…”

“…The temperature-dependent characteristic field describing the exponential decay was found to show only small variations from one Bi,Pb(2223) tape to another, irrespective of its overall critical current ( ) [1]. Furthermore, by properly taking into account experimental differences, this high-field behavior is essentially identical to the magnetic response not only of the tapes, but also of Bi,Pb(2223) powders prepared in different ways [2].…”

Intragranular and intergranular behaviour of multifilamentary Bi-2223/Ag tapes

“…Each technique brings out specific information on intragranular critical currents (J cG ) or intergranular critical currents (J cJ ), and their comparison is helpful in elucidating the current limitation processes in HTS tapes [8]. A particular emphasis will be placed on understanding the importance of connectivity and anisotropy of the critical currents through estimating the J cG ab /J cJ ab and J cJ ab /J cJ c ratios.…”

Role of c-axis field components in making the transport E(J) characteristics of (Bi,Pb)2Sr2Ca2Cu3Ox tapes insensitive to the direction of field within the tape plane

“…It is widely recognized that multiple parallel current paths exist in real tapes. [5][6][7][8] Magneto-optical images provide direct evidence of these percolative current paths, 9 but generally lack the spatial resolution to distinguish between particular percolation paths. Such percolative current flow means that the local current vector is often quite different from the macroscopic one.…”