Grain boundaries in Bi-2223/Ag composite tapes were investigated by using atomic-resolution Z-contrast imaging in a scanning transmission electron microscope. It was found that one of the most prevalent types of boundary between the superconductor grain colonies was a c-axis twist boundary which was located at the middle of the double BiO layers. No amorphous layers were found at these boundaries, but local phase variations were frequently observed at, or near to, the boundaries. Another typical grain boundary was the small-angle asymmetrical tilt boundary, which was parallel to the basal planes of a given grain. At small-angle asymmetrical tilt boundaries, various types of phase – with various numbers of CuO2 layers in their unit cell - formed periodically along the boundary plane. Consequently, this type of boundary also occurred at the middle of the BiO double layers. These local phase variations existed close to the Ag interface, and could give rise to weak-link behavior. In addition, many dislocations and stacking faults were observed within the filaments.

Direct Atomic Scale Imaging of Grain Boundaries and Defects in Bi-2223/Ag High-Tc Superconducting Tapes. K.Kishida, N.D.Browning: Physica C, 2001, 351[3], 281-94