JOURNAL OF SOLID STATE CHEMISTRY 77, 316-321 (1988) Structure Determination of Ca4Fe2Ti2011 by Electron Microscopy and Crystallographic Image Processing SVEN HOVMGLLER, XIAODONG ZOU, AND DA NENG WANG Structural Chemistry, University of Stockholm, S-106 91 Stockholm, Sweden AND JOSE MARIA GONZALEZ-CALBET AND MARIA VALLET-REGi Inorganic Chemistry, Complutense University, Madrid 280 40, Spain Received May 4, 1988 The crystal structure of Ca4FezTi201, has been determined by high-resolution electron microscopy and crystallographic image processing. The space group is Prima. The Perovskite-type structure is composed of MeO, octahedra and MeO, tetrahedra, arranged as OOOTOOOT along the long b-axis of the crystals. 0 1988 Academic Press, Inc. Introduction Perovskite-related oxides, AMOj..., are now at the center of interest because some of them have shown superconducting prop- erties at high temperatures (I, 2). Since Wadsley (3) predicted the existence of ordered phases between the perovskite (AMOS) and the brownmillerite (AMO& structural types, many efforts have been made to obtain such materials. A detailed knowledge of the atomic structures of these materials is essential for a better compre- hension of their properties. Many of these compounds are difficult to prepare as single crystals large enough to be studied by X-ray diffraction. For these HREM, electron diffraction, and X-ray powder diffraction (4) a structural model was proposed, with alternating MeO6 octa- hedra and Me04 tetrahedra, arranged as OOOTOOOT. . . The space group was not determined, but the crystals were consid- ered orthorhombic with a = 5.437(l), b = 30.22(l), and c = 5.489(l) A. It has been shown that HREM combined with crystallographic image processing (CIP) can be used to determine coordinates of metal atoms in oxides with an accuracy of about 0.1 A (5, 6). In order to determine if the earlier proposed model of &Fe, Ti20i1 was correct, we applied CIP on the HREM images of the structure. high-resolution - electron . microscopy Materials and Methods (HREM) is the most suitable method for obtaining structural information at the unit The preparation of Ca4Fe2Ti201i and the cell level. The perovskite-related oxide electron microscopy were described earlier Ca4Fe2Ti20i1, the n = 4 member in a series (4). The same HREM images and electron having the general formula A,M,Oj,-I is diffraction patterns that were published in one of these cases. (4) were used in the present investigation. In a previous study of this compound by In addition the (hk0) electron diffractogram 0022-4596/88 $3.OO 316 Copyright 0 1988 by Academic Press, Inc. All rights of reproduction in any form reserved.