Superstructure of the Superconductor Bi2 Sr2 CaCu2 O8 by High Resolution Electron Microscopy

摘要

The superstructure of the high Tc superconducting oxide Bi/sub 2/Sr/sub 2/CaCu/sub 2/0/sub 8/ has been studied by high resolution electron microscopy. Waves of distortion along the b-axis give an incommensurate superlattice slightly larger or smaller than 5 sqrt 2a /sub p/ (a/sub p/ = perovskite unit cell). The building blocks along the b-axis are 4, 5 and 6 times sqrt 2a/sub p//2. The incommensurate superlattice is composed of approximately periodic combinations of these building blocks. The symmetry of three major projections are P/sub gm/ (or possibly P/sub gg/), C/sub mm/ and C/sub mm/ for the ideal superlattice with b=5 sqrt 2a/sub p/. These projections correspond to the space groups Pcnn and Pmnn respectively. (ERA citation 14:015240)