We report on the structure and characterization of the major phase in the Bi-Sr-Ca-Cu-O system that becomes superconducting below 80 K. A superlattice modulation in the structure that is incommensurate with a tetragonal perovskite-based subcell is observed using electron diffraction. High-resolution imaging indicates that the modulation occurs primarily in bismuth-rich layers in the structure.

• Received 12 February 1988

DOI:https://doi.org/10.1103/PhysRevB.37.9856