The layered sodium cobalt oxide NaxCoO2 is studied by electron diffraction for a wide range of sodium contents, 0.15<x<0.75. An extensive series of ordered Na ion-Na vacancy superlattices is found beyond the simple hexagonal average structure. The most strongly developed superlattice is found for the composition Na0.5CoO2, which displays Co3+/Co4+ charge ordering at low temperatures. The structural principle for some of the observed ordering schemes, particularly, near x=0.5, is, surprisingly, the presence of lines of Na ions and vacancies rather than simply maximized Na-Na separations.
|Physical Review B - Condensed Matter and Materials Physics
|Published - Jul 2004
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics