OXIDATION-PRODUCTS OF NB4W13O47 - A TRANSMISSION ELECTRON-MICROSCOPY STUDY

Nb4W13O47, a mixed valency oxide crystallizing in the structure of the 4:9 phase (4Nb(2)O(5) . 9WO(3)), was oxidized at various temperatures . The products have been characterized by high-resolution transmission electron microscopy. Oxidation products obtained at 600 and 1000 degr ees C exhibit the development of planar defects running along {110} of the TTB subcell. The defects are built up by structural elements obse rved here for the first time: Two or more five-membered rings of octah edra are connected via two common octahedra. These arrays are combined with blocks of ReO3-type structure and ordered along the defect plane s. The oxidation at 1200 degrees C leads to a separation into the 2:7 phase and WO3. (C) 1995 Academic Press, Inc.