structure of the Pseudorhombohedral InFe_1-xTi_xO_3+x/2 composite crystal

Yuichi Michiue,^a Mitsuko Onoda,^a Francisco Brown,^b Noboru Kimizuka,^c and Mamoru Watanabe^a

^aAdvanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, 305-0044, Japan; ^bDepartamento de Investigaciones en Polimeros y Materiales, Universidad de Sonora, Rosales s/n Hermosillo, Sonora, C.P.83000, Mexico; ^cCeramic Materials Research Institute, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea (MICHIUE.Yuichi@nims.go.jp)

In pseudobinary systems InAO₃-In₂Ti₂O₇ (A:Fe, Ga, Al, Cr), composite crystals InA_1-xTi_xO_3+x/2 with two types of layered structures were found [1]. The one obtained in the Ti-rich region has the pseudorhombohedral (p-R) structure and the other in the A-rich region does the pseudohexagonal (p-H). The incommensurately modulated structure of the p-H InFe_1-xTi_xO_3+x/2 was clarified by the 4-dimensional superspace group analysis for diffraction data of a single crystal [2]. In this paper the structure of the p-R form is discussed on the basis of the profile fitting of X-ray diffraction patterns.

The structure of a commensurate (x=2/3) p-R form for A=Fe is shown in Fig. 1. In analogy with the p-H form, the p-R phases are also described as the composite crystal consisting of the two subsystems with different periods along the b-axis. The first subsystem is constructed by InO₆ octahedral sheets and the Fe/Ti atoms in a slab at z=0.5, while the second one is made only by the O atoms in the slab containing the Fe/Ti atoms. Atomic arrangement in the slab is given in Fig. 2, which is similar to that seen in a part of the p-H structure [2].

References

1 Brown, F., Flores, M. J. R., Kimizuka, N., Michiue, Y., Onoda, M., Mohri, T., Nakamura, M. and Ishizawa, N. (1999) J. Solid State Chem. 144, 91-99.

2 Michiue, Y., Onoda, M., Watanabe, M., Brown, F. and Kimizuka, N. (2001) Acta Crystallogr. B57, 458-465.