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-sheathe d 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 colo ny are piled up along the common c-axis and are separated by [001] twi st boundaries. It was found that the rotation angle of these twist bou ndaries takes several definite values. Colony boundaries are formed be tween colonies having slightly tilted c-axes with respect to each othe r and are virtually free from amorphous material and intergranular pha ses, Two basic types of colony boundaries have been observed: the smal l-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 c oncerning the formation of colony boundaries is discussed.