ON THE VIBRATIONAL-SPECTRA AND STRUCTURE OF FECRO3 AND OF THE ILMENITE-TYPE COMPOUNDS COTIO3 AND NITIO3

The XRD patterns and the IR and Raman spectra of fine powders of the corundum-type sesquioxides alpha-Fe2O3 and alpha-Cr2O3, of the ilmenite-type mixed oxides NiTiO3 and CoTiO3 and of the mixed oxide alpha-FeCrO3 is obtained from the XRD pattern, the IR and Raman spectra provide evidence for the centrosymmetric ilmenite-type superstructure in the case of alpha-FeCrO3. The noncentrosymmetric alternative superstructure (LiNbO3-like) is excluded by the validity of the mutual exclusion rule. (C) 1994 Academic Press, Inc.