Structure Determination of Two New Incommensurate Compounds, Ba_1+x[(Cu_xRh_1-x)O₃] with x = 0.1605 and x = 0.1695, Using a General Method Based on the Superspace Group Approach

Abstract

The single-crystal structures of two incommensurate compounds, Ba 1+x [(Cu x Rh 1-x )O 3 ] with x ) 0.1605 and x ) 0.1695, were solved by a general method using the superspace group approach. A saw-tooth function was used to model both the occupational and displacive modulations. This approach requires very few refineable parameters and leads to low residuals, R ) 0.0370 and R ) 0.0330 for x ) 0.1605 and x ) 0.1695, respectively. The idealized structures of these two compounds consist of [(Cu x Rh 1-x )O 3 ] ∞ chains containing groups of five face-shared (RhO 6 ) octahedra separated by (CuO 6 ) trigonal prisms. These chains in turn are separated from each other by [Ba] ∞ chains. The idealized composition of both phases is Ba 7 CuRh 5 O 18 . Their modulated structures, described in the text, deviate from the ideal composition and structure. The approach used for the structure determinations of these compounds is completely general and can be applied to other modulated composite structures of this series.

Electron diffraction evidence for continuously variable, composition-dependent O/F ordering in the ReO3 type, NbV1−xNbIVxO2−xF1+x, 0⩽x⩽0.48, solid solution

“…To model the corresponding real space occupation modulation of the z/001S (z an integer) anion sites along the three /001S directions, a one-dimensional, crenel (square wave) type function [15,16] has been used. Thus, we have assumed that each anion site can only be occupied by either an O or an F, i.e.…”

Sr3NiRhO6 and Sr3CuRhO6—Two New One-Dimensional Oxides. Magnetic Behavior as a Function of Structure: Commensurate vs Incommensurate

“…One is the incorporation of extra oxygen into a trigonal prismatic site, resulting in the conversion of one trigonal prismatic site into two octahedral sites, giving rise to a net gain in oxygen for the material. Another potential process involves the migration of [A] chain cations into the transition metal [ (A, B) (1,12,13,39). The composition is directly related to the value by the relationship "(1#x)/2 where "c /c (11,13).…”

Crystal growth, structure determination and magnetism of a new m=3, n=1 member of the A3n+3mA′nB3m+nO9m+6n family of oxides: 12R-Ba12Rh9.25Ir1.75O33

“…the two end members of this family of oxides. The compounds can also be described as modulated composite structures, where the structure is depicted as two mutually interacting subsystems modulated along z but periodic in the xy plane [8,9,[12][13][14].…”