Critical current limiting factors in post annealed (Bi; Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tapes

Abstract

Abstract-Processing

Significantly enhanced critical current density in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox composite conductors prepared by overpressure processing in final heat treatment

“…In fact, the value of 0.11 is the smallest 2212 SQUID index that we have measured for 2223 samples from a variety of sources. 2,10,20 J c was enhanced by reduction of cross-section area and by improved connectivity. OP processing reduced porosity and cracking from ϳ20% of the cross-section area in the FHT and FHTϩ1b samples to less than 5% in the FHT ϩOP sample, which proportionally enhanced the active cross-section area that carried current.…”

“…This as-rolled tape subsequently goes through a thermomechanical cycle that consists of a first heat treatment ͑HT1͒, an intermediate rolling ͑IR͒, and a final heat treatment ͑FHT͒. The FHT includes a second heat treatment ͑HT2͒ and a separate low temperature ''post anneal'' ͑PA͒ or a heat treatment combining HT2 and PA. 9,10 About 80% of the precursor oxide powder reacts to 2223 phase in HT1. IR helps densify the superconducting filaments while HT2 and any FHT further increase 2223 formation.…”

“…2,15,16 Increases in J c were found to correlate strongly with decreases in the volume fraction of 2212. 2,10,15 A central question in further improving the performance of 2223 tapes is how to eliminate the current limiting mechanisms of porosity, cracks, and residual 2212 to further improve the J c .…”

“…The broadening and kink at ϳ80 K are both thought to be caused by 2212 in the sample that is exposed when the 2223 is crushed in the rolling process. 2,10,20 A method has been proposed 2,10,20 to evaluate the relative amount of 2212 in the tape, which defines a 2212 SQUID index. As shown in Fig.…”

Irreversibility fields of Bi-2223 at 30-77 K

“…The connectivity contribution to is not easy to define, though detailed magneto-optical current reconstructions are making this parameter much clearer [11]. In recent work, it has been shown that minimization of 2212 intergrowths is very valuable in raising (0 T, 77 K) and (0.1 T, 77 K), probably because such intergrowths strongly reduce the current path cross-section at 77 K [4]- [6]. However, 2212 intergrowths are only one of many current-limiting mechanisms controlling the of Bi-2223 tapes.…”