Preparation, characterization and reactivity toward oxygen of new nanosized vanadium-iron spinels

Different series of nanosized VxFe3-xO4 (0 less than or equal to x less than or equal to 2) spinels have been prepared by a soft chemistry method in 0.5x intervals and studied by X-ray diffraction, infrared spectrometry and thermogravimetry. It has been established that these finely divided powders (crystallite size approximate to 60 nm), with general (Fealpha2+Fe1-alpha3+)(A)(Fe1-alpha2+Fe1-x3+Vx3+)(B)O-4(2-) formula can be oxidized between 100 and 550 degrees C while retaining the spinel structure. Based on a quantitative determination of the cation distribution on the octahedral (B) and tetrahedral (A) sites, by derivative thermogravimetry, it has been found that Fe-B(2+),V-B(3+) and Fe-A(2+) ions are successively oxidized into Fe3+ and V5+ ions. As a result of the oxidation, the vanadium-iron cation-deficient spinels may have a very high number of vacancies located on B sites. This one may reach 0.90 for x = 2. (C) 1998 Elsevier Science B.V. All rights reserved.