Effect of hot uniaxial pressing on the microstructure and critical current density of (Bi, Pb)-2223 tapes

Pressures up to 10 MPa were applied uniaxially to (Bi, Pb)2Sr2Ca2Cu3Oy ((Bi, Pb)-2223) tapes during either the first or second stage of the heat treatment process in air. After both annealing stages, an increase of the oxide filament density of the tapes was observed when applying pressure. For the first stage, the critical current (Ic) of the tapes was very sensitive to the applied pressure, and the reproducibility was poor. This behaviour is related to the large amount of liquid involved in the reaction. This liquid was easily pushed out from the centre to the edges of the tapes by pressure, which caused local deviations of the composition and hence, a decrease of volume fraction of (Bi, Pb)-2223. In contrast, applying pressure only during the second stage when a moderate amount of liquid is produced brought about the high densification and the reproducible enhancement of Ic and critical current density (Jc) values by about 40 and 100%, respectively. This enhancement is attributed to the high densification and improved coupling of grains due to the uniaxial pressure