CHEMICAL AND STRUCTURAL-PROPERTIES OF THE SYSTEM FE2O3-CR2O3

Chemical and structural properties of the mixed metal oxides (1 - x) Fe2O3 + xCr2O3 were studied by different techniques. X-ray powder diffraction showed the existence of solid solutions, (Fe1-xCrx)2O3, over the whole concentration region, 0 less-than-or-equal-to x less-than-or-equal-to 1. The gradual replacement of Fe3+ with Cr3+ ions in samples prepared at 900-degrees-C caused changes in unit-cell parameters; most of these changes took place in the region from x almost-equal-to 0.3-0.9. The samples having the fraction of Cr2O3 in the region from approximately 0.7-0.8, contained two closely related phases, with slightly different compositions. After an additional heat treatment at 1100-degrees-C, these samples contained only one phase. Fe-57 Mossbauer spectroscopy showed a gradual decrease of hyperfine magnetic field with increasing Cr2O3 content. The sample having the fraction of Cr2O3 of 0.7, and prepared at 900-degrees-C, exhibited two separated sextets at room temperature, in comparison with other compositions showing one sextet. It was shown that Fourier transform infrared (FT-IR) spectroscopy is a powerful method for the investigation of structural changes in these solid solutions. The increase in the Cr2O3 content resulted in shifts of the corresponding infrared bands. In addition, a gradual transition of the spectrum typical for alpha-Fe2O3 to the spectrum typical for Cr2O3 was shown. The transition effects observed in the FT-IR spectra were correlated with the X-ray powder diffraction and Fe-57 Mossbauer spectroscopic results.