ORDERING OF ANIONIC VACANCIES IN THE BACOO2.94 HEXAGONAL RELATED PEROVSKITE

An electron diffraction and high-resolution electron microscopy study shows that oxygen vacancies in BaCoO2.94 lead to a threefold superstru cture along the (11(2) over bar 0)(2H) direction, the ...hhh... hexago nal sequence characteristic of the 2H type being maintained. According to compositional and structural data, the most probable structural mo del should be formed by three AO(3) layers intergrowing with one AO(2. 67) layer along the c-axis. In such oxygen-deficient layers, one of ea ch six oxygen atoms in every oxygen row is removed, leading to the obs erved superstructure. (C) 1997 Academic Press.