TEM study of twist boundaries and colony boundaries in (Bi,Pb)2Sr2Ca2Cu3Ox silver-sheathed tapes

Abstract The grain boundaries in high- j c (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x 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 Bi 2 Sr 2 Ca n −1 Cu n O x and their importance concerning the formation of colony boundaries is discussed.