Acta Crystallographica Section B

Structural Science

Volume 57, Part 4 (August 2001)

research papers

Acta Cryst. (2001). B57, 458-465 [ doi:10.1107/S0108768101005432 ]

Modulated structure of the pseudohexagonal InFe_1-x-4Ti_x+3O_3+x/2 (x = 0.61) composite crystal

Y. Michiue, M. Onoda, M. Watanabe, F. Brown and N. Kimizuka

Abstract: The structure of pseudohexagonal-type InFe_1-x-4Ti_x+3O_3+x/2 (x = 0.61, [delta] = 0.04), indium iron titanium oxide, was refined on the basis of a four-dimensional superspace group. The crystal has a compositely modulated structure consisting of two orthorhombic subsystems mutually incommensurate in b. The first subsystem InFe_1-x-4Ti_x+3O₂ has a delafossite structure with lattice parameters a = 5.835 (3), b₁ = 3.349 (1) and c = 12.082 (7) Å. The second subsystem with b₂ = 2.568 (6) Å consists of O atoms. The superspace group of the overall structure is Ccmm(1, 1.305, 0)s00, which can be converted to Amam(0, 0, 0.305)0s0 (No. 63.8). Refinement on 1105 unique reflections converged to R = 0.0303 and wR = 0.0325 with 63 structural parameters. The structure of the first subsystem is the alternate stacking of an edge-shared InO₆ octahedral layer and an Fe/Ti triangle-lattice plane along c. A sheet of O atoms in the second subsystem is also extending on the Fe/Ti plane, where displacive modulation of atoms is prominent.

Keywords: modulated structure; composite crystal; pseudohexagonal.