Ceramics-Silikáty 47 (1) 32-39 (2003)

Fe₂O₃-Cr₂O₃ SYSTEM REVISED

T. Grygar, P. Bezdička, J. Dědeček, E. Petrovský, O. Schneeweiss

Hematite (a-Fe₂O₃) and eskolaite (Cr₂O₃) are typical examples of isostructural oxides with non-linear change of the lattice parameters in their solid solutions. This series was synthesized and characterized by X-ray and neutron powder diffraction, and Mössbauer and electronic spectroscopies. A region of the d-d electron transition of Fe(III) ions in near IR region (about 1000 nm) were found to be suitable for the solid solution characterization, because the transition does not suffer from strong overlaps of Fe(III) and Cr(III) transitions in electronic spectra in the Vis spectral range. Lattice parameters, verified by the comparison to data available in literature, showed that in several cases in the last decade solids of questionable quality were obtained and discussed in the hematite-eskolaite system. Neither X-ray nor neutron diffraction indicated cation ordering, hypothesized in two reports in 1990's. Magnetic structure of the solid solution at 0 < x < 0.6, where x = Cr/(Cr + Fe), is similar to that of hematite, but a different, yet unidentified magnetic ordering involving Fe(III) ions is established in solid solution x = 0.8 below its Néel temperature (about 150 K).

Keywords: Solid solutions, Vegard law, Iron oxide, Chromium oxide