High-Resolution Electron Microscopy of Modulated Structure in 20 K Superconducting Oxide Bi2Sr2CuOy

Abstract

The structure of the 20 K superconductor Bi₂Sr₂CuO _y is examined by high-resolution transmission electron microscopy. A strongly modulated structure due to the periodic lattice distortions is observed. The unit cell is B-centered monoclinic with a _m=0.54, b _m=2.6, c _m=2.8 nm and α=116°, where b _m is incommensurate with the tetragonal subcell. The pseudo-orthorhombic setting of the unit cell, where A=a _m=0.54, B=b _m=2.6 and C=2c _m cos α=5.0 nm, reported previously [Matsui et al.: Jpn. J. Appl. Phys. 27 (1988) L827], is considered convenient to compare the superstructure with the orthorhombic one of the 80 K superconductor Bi₂Sr₂CaCu₂O _y .