Antiphase Modulated Structure of Fe2O3(ZnO)15Studied by High-Resolution Electron Microscopy

As one of our systematic studies of the modulated structures of a series of new homologous compounds RM O 3 (ZnO) m ( R =Sc, In, Y, and La; M =In, Fe Ga, and Al; m =integer), this paper reports the modulated structure of Fe 2 O 3 (ZnO) 15 ( R =Fe; M =Fe) studied by high-resolution electron microscopy. It is found that the main and satellite spots in the diffraction patterns can be indexed as h a * + k b * + l c * + m q by considering a monoclinic unit cell of a =0.57 nm, b =0.33 nm, c =4.5 nm, and β =92° and a modulation wave vector of q=b * /34.8+c * /2. The possible space groups for the basic structure are C 2, Cm , and C 2/ m , and the possible four-dimensional superspace groups for the modulated structure are C C 2 1 , C Cm 1 , and C C 2/ m 1 1 . The crystal structure of Fe 2 O 3 (ZnO) 15 consists of Fe–O layers interleaved with 16 Fe/Zn–O layers. In the high-resolution image, the modulated structure appeared as zigzag-shaped contrasts among the Fe/Zn–O layers, where Fe is in high concentration. Compared with those of In M O 3 (ZnO) m ( R =In; M =In, Fe and Ga) reported in our earlier paper, the special features of the present modulated structure are the half-periodicity relative shift of the neighboring zigzag-shaped contrasts and the appearance of modulation within the Fe–O layers.