STRUCTURAL AND MORPHOLOGICAL-CHANGES ASSOCIATED WITH CHARGE ORDERING IN LA0.2CA0.8MNO3

Both structural and morphological changes associated with charge order ing in perovskite manganese oxide, La0.2Ca0.8 MnO3, were studied by el ectron microscopic observations with imaging plates. Two types of long -period structures were observed at around 107 K, i.e., the structure with about 4-fold periodicity to the unit lattice distance of the room -temperature phase and the structure with much larger periodicity such as 23-fold. These long-period structures were suggested to be formed by a similar mechanism due to charge ordering of manganese ions, since they showed some crystallographic and morphological similarities. Sup erlattice reflections of a near 4-fold structure were observed as a fu nction of temperature. They were found to become weak diffuse scatteri ng just before the disappearance, and the peak positions moved slightl y with heating. Considering those features, the kinetics of the charge ordering in this oxide was discussed. (C) 1998 Academic Press.