engleski

Formation And Characterization Of The Solid Solutions (CrxFe1-x)2O3, 0-Less-Than-Or-Equal-To- x-Less-Than-Or-Equal-To-1

The solid solutions (CrxFe1-x)(2)O-3, 0 less than or equal to x less than or equal to 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, Mossbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, alpha-(CrxFe1-x)(2)O-3, which is isostructural with alpha-Fe2O3 and phase C, which is closely related to Cr2O3. Phase F exists in samples heated up to 900 degrees C, for 0 less than or equal to x less than or similar to 0.95. Phase C exists from x greater than or similar to 0.27 to x = 1 for samples heated up to 900 degrees C and from x greater than or similar to 0.65 to x = 1 for samples heated up to 1200 degrees C. For samples heated up to 900 degrees C, the solubility limits were 27.5 +/- 0.5 mol% of Cr2O3 in alpha-Fe2O3 and 4.0 +/- 0.5 mol% of alpha-Fe2O3 in Cr2O3. For the samples heated at 1200 degrees C the diffraction peaks for the F and C phases in the two phase region were severely overlapped and thus the solubility limits could not be determined accurately as for previous samples. Fe-57 Mossbauer spectra of the samples heated up to 1200 degrees C showed significant broadening of spectra lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x greater than or similar to 0.7, a paramagnetic doublet with collapsing sextet was observed. The spectra were interpreted in terms of an electronic relaxation effect ; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect could not be excluded. The FT-IR spectra showed transition effects in accordance with the X-ray diffraction results. The mostintense absorption bands, observed for the samples heated up to 1200 degrees C, were located at similar to 460 and 370 nm (22 000 and 27 000 cm(-1)) for x greater than or equal to 0.5, similar to 500 and 360 nm for x < 0.3, and might be correlated with the strong enhancement of the pair transitions through antiferromagnetic interactions. The intensification of the (6)A(1) - -> T-4(1) Fe3+ ions in all spectra and the development of the absorption at 13 000 cm(-1) due to a metal-metal charge transfer (Cr3+ --> Fe3+) transition, might be explained by exchange coupling which has been observed in some spinel compounds.[References: 33]

Solid-solutions ; Structural-properties ; Optical-absorption ; Spinel structure ;

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