The structure of Ba1.1064CoO3 has been solved in the (3 + 1)-dimensional fo
rmalism. The structure is described as a modulated chain composite with two
subsystems, [Coos] and [Ba], respectively. The superspace group is R-3m (0
0 gamma )0s with a = 9.8842(20) Angstrom, c = 2.4785(12) Angstrom, and q =
0.5532(4) c* (Z = 3). A saw-tooth function was used to model both the occup
ational and displacive modulations. Each atomic saw-tooth function is defin
ed by its center (x) over cap (4), along the fourth dimension, its width (A
), and the maximum amplitude of the displacive modulation (delta). The pape
r describes how, as a first approximation, the columns (CoO3) can be mainly
described by a single free parameter, based on the height difference of th
e trigonal prisms and octahedra that constitute the transition metal chains
. As a result, this superspace formalism requires only a small number of va
riables to be refined, compared to the conventional superstructure descript
ion. (C) 2001 Academic Press.