TEM Study of twist boundaries and colony boundaries in (Bi,Pb)(2)Sr2Ca2CU3Ox silver-sheathed tapes

The grain boundaries in high-j(c) (Bi,Pb)(2)Sr2Ca2Cu3Ox silver-sheathed tapes have been investigated using transmission electron microscopy, The typical microstructural feature in these tapes are the colonies, which consist of grains with a common c-axis. The grains within a colony are piled up along the common c-axis and are separated by [001] twist boundaries. It was found that the rotation angle of these twist boundaries takes several definite values. Colony boundaries are formed between colonies having slightly tilted c-axes with respect to each other and are virtually free from amorphous material and intergranular phases, Two basic types of colony boundaries have been observed: the small-angle c-axis tilt boundary and the edge-on c-axis tilt boundary, The weak bonds between the BiO double layers are responsible for the mica-like crystalline structure of Bi2Sr2Can-1CunOx and their importance concerning the formation of colony boundaries is discussed.