High-Resolution Electron Microscopy of Modulated Structure in 20 K Superconducting Oxide Bi₂Sr₂CuO_y

Abstract

The structure of the 20 K superconductor Bi 2 Sr 2 CuO 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 =2 c 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 Bi 2 Sr 2 CaCu 2 O y .