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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≤x≤1. The gradual replacement of Fe3+ with Cr3+ ions in samples prepared at 900°C caused changes in unit-cell parameters ; most of these changes took place in the region from x≈0.3-0.9. The samples having the fraction of Cr2O3 in the region from ∼0.7-0.8, contained two closely related phases, with slightly different compositions. After an additional heat treatment at 1100°C, these samples contained only one phase.57Fe Mössbauer 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°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 α-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 and57Fe Mössbauer spectroscopic results.

iron oxides ; chromium oxides ; Mossbauer spectroscopy ; phase transitions ; solid solutions ; X ray analysis

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