VACANCY ORDERING IN GAMMA-FE2O3 - SYNCHROTRON X-RAY-POWDER DIFFRACTION AND HIGH-RESOLUTION ELECTRON-MICROSCOPY STUDIES

This paper reports synchrotron X-ray powder diffraction and high-resol ution electron microscopy studies of the structural arrangement in gam ma-Fe2O3. Powder diffraction data as well as high-resolution electron microscopy show that the basic structure of gamma-ferric oxide possess es cubic symmetry (space group P4(3)32), whereas the ordered distribut ion of the cation vacancies on the octahedral positions results in the formation of the tetragonal superlattice (space group P4(1)2(1)2). Th e character of the superstructure orientation with respect to the deve loped planes of the gamma-Fe2O3 microcrystals obtained by different pr eparative techniques is also discussed.