Modulated Structures of Homologous Compounds InMO3(ZnO)m(M=In, Ga;m=Integer) Described by Four-Dimensional Superspace Group

Abstract

The modulated structures appearing in the homologous compounds InMO3(ZnO)m(M=In, Ga;m=integer) were observed by using a high-resoultion transmission electron microscope and are described based on a four-dimensional superspace group. The electron diffraction patterns for compounds withmlarger than 6 reveal extra spots, indicating the formation of a modulated structure. The subcell structures form=odd and even numbers are assigned to be either monoclinic or orthorhombic, respectively. On the other hand, extra spots can be indexed by one-dimensional modulated structure. The possible space groups for the subcell structure areCm,C2, andC2/mform=odd numbers, while those form=even numbers areCcm21andCcmm, respectively. Then, corresponding possible superspace groups are assigned to bePC2s,PCm1, andPC2/ms1for oddmnumbers andPCcm21111andPCcmm111for evenmnumbers. Based on the superspace group determination, a structure model for a one-dimensional modulated structure is proposed. © 1998 Academic Press.