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 compoundsRMO3(ZnO)m(R=Sc, In, Y, and La;M=In, Fe Ga, and Al;m=integer), this paper reports the modulated structure of Fe2O3(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 asha*+kb*+lc*+mq by considering a monoclinic unit cell ofa=0.57 nm,b=0.33 nm,c=4.5 nm, and BETA =92° and a modulation wave vector of Q=b*/34.8+c*/2. The possible space groups for the basic structure areC2,Cm, andC2/m, and the possible four-dimensional superspace groups for the modulated structure areCC21,CCm , andCC2/m1 . The crystal structure of Fe2O3(ZnO)15consists 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 InMO3(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.