Effect of the phase compositions at the final stage of heat treatment on the critical current density in Bi:2223/Ag tapes

Abstract

The effect of the phase compositions after the final stage of heat treatment on the critical current density in Bi:2223/Ag tapes has been investigated. A high volume fraction of Bi:2223 has been considered the most critical factor in achieving a high ; however, it is extremely difficult to attain pure Bi:2223 phase via routine thermomechanical processing. Although a higher volume fraction of Bi:2223 phase can be attained using a higher processing temperature, it is always found to co-exist with Bi:2201 which resides at Bi:2223 colony boundaries. As these possess a plate-like morphology, the Bi:2201 joins weak links in a conductible chain. Bi:2201 can be eliminated using an annealing step at the end of the last thermal cycle, resulting in a significant improvement in . At annealing temperatures below , Bi:2223 decomposes into Bi:3221 and other cuprates, which degrade further. Magnetization, AC susceptibility and resistivity measurement results confirm that the Bi:2201 and Bi:3221 act as weak links.