STUDY ON INTERFACES AND MICROSTRUCTURAL DEFECTS IN AG-CLAD (BI,PB)(2)SR2CA2CU3O10+Y TAPES

The interfaces and microstructural defects in the broad face and longi tudinal cross-sectional specimens of Ag-sheathed (Bi, Pb)(2)Sr2Ca2Cu3O 10+y (2223) tapes have been studied by TEM. Most of the twist boundari es in the colonies have a small rotation angle, accommodated by a scre w dislocation network. The twist boundaries are normally atomically fl at without a second phase. Most of the colony boundaries are of mixed type with a misorientation angle up to 30 degrees. A thin amorphous la yer is commonly formed at colony boundaries with adjacent basal planes on both sides of the boundary. Most of the c-direction colony boundar ies are mixed-type ones, and second phases were sometimes observed at these boundaries. Tilt boundaries, consisting of a wall of edge disloc ations, are clean and the lattices from both sides of the boundary are well matched. At the triple colony junction, second phases were often found. Around a large isolated particle of a second phase, small colo nies were found to be randomly orientated and seriously distorted. The [001] edge dislocations, and the bend and interruption of the (001) p lanes were often observed. A systematic study on the correlation betwe en J(c), and 2212 fraction in numerous tapes shows that tapes with hig her J(c) always contain a certain fraction of 2212 phase, while the ta pes with a very low fraction of 2212 did not show high J(c). These res ults seem to indicate that the predominant weak links in the tape are not 2212 layers at twist boundaries in the low 2212 fraction regime. T he predominant weak links in tapes are colony boundaries and J(c) is a ssumed to be controlled by colony boundaries in low fields.