FORMATION AND CHARACTERIZATION OF THE SOLID-SOLUTIONS (CRXFE1-X)(2)O-3, 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 t han or equal to 1, were prepared by traditional ceramic procedures. Th e samples were characterized using X-ray diffraction, Mossbauer, Fouri er transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, alpha-(Crx Fe1-x)(2)O-3, which is isostructural with alpha-Fe2O3 and phase C, whi ch 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 f or samples heated up to 900 degrees C and from x greater than or simil ar to 0.65 to x = 1 for samples heated up to 1200 degrees C. For sampl es 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 C r2O3. For the samples heated at 1200 degrees C the diffraction peaks f or 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 doubl et with collapsing sextet was observed. The spectra were interpreted i n terms of an electronic relaxation effect; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect co uld not be excluded. The FT-IR spectra showed transition effects in ac cordance with the X-ray diffraction results. The most intense absorpti on bands, observed for the samples heated up to 1200 degrees C, were l ocated at similar to 460 and 370 nm (22 000 and 27 000 cm(-1)) for x g reater than or equal to 0.5, similar to 500 and 360 nm for x < 0.3, an d might be correlated with the strong enhancement of the pair transiti ons through antiferromagnetic interactions. The intensification of the (6)A(1) --> T-4(1) Fe3+ ions in all spectra and the development of th e absorption at 13 000 cm(-1) due to a metal-metal charge transfer (Cr 3+ --> Fe3+) transition, might be explained by exchange coupling which has been observed in some spinel compounds.