STRUCTURAL FEATURES OF BA4FE4TI3O16 AND BA26FE20TI21O98 AS REVEALED BY HIGH-RESOLUTION ELECTRON-MICROSCOPY

Preliminary results from high-resolution microscopy and electron diffr action studies of two new compounds with approximate compositions Ba4F e4Ti3O16 (E phase) and Ba26Fe20Ti21O98 (M phase) are described. The co mpounds were found to be structurally related and exhibit two types of structural blocks. One of the blocks (H) is ordered with respect to t he other by tripling within the basal hexagonal cell. Another block (P ) is apparently perovskite-related. Phase E was found to have a well-o rdered structure (space group either hexagonal P6 or trigonal P3), whe reas phase M exhibits persistent and regularly occurring structural di sorder as revealed by the presence of diffuse, continuous streaks. We suggest that the origin of this disorder is poor correlation in transl ation of the H blocks. (C) 1996 Academic Press,Inc.