ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The solid solutions (CrxFe1−x)2O3, 0 ⩽ x ⩽ 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, Mössbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, α-(CrxFe1−x)2O3, which is isostructural with α-Fe2O3 and phase C, which is closely related to Cr2O3. Phase F exists in samples heated up to 900°C, for 0 ⩽ x ≲ 0.95. Phase C exists from x≳0.27 to x=1 for samples heated up to 900°C and from x≳0.65 to x=1 for samples heated up to 1200 °C. For samples heated up to 900 °C, the solubility limits were 27.5 ± 0.5 mol% of Cr2O3 in α-Fe2O3 and 4.0 ± 0.5 mol % of α-Fe2O3 in Cr2O3. For the samples heated at 1200 °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. 57Fe Mössbauer spectra of the samples heated up to 1200 °C showed significant broadening of spectral lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x≳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 most intense absorption bands, observed for the samples heated up to 1200 °C, were located at ∼ 460 and 370 nm (22 000 and 27 000cm−1) for x⩾ 0.5, ∼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 6A1 → 4T1 Fe3+ ions in all spectra and the development of the absorption at 13000 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00352669
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