XPS and EELS investigations of chemical homogeneity in nanometer scaled Ti-ferrites obtained by soft chemistry

Nanocrystalline Ti-ferrites with composition Fe3-xTixO4 with 0 less than or equal to x less than or equal to 1 are synthesized using the soft chemistr y route. Heterogeneities in precipitate and annealed powders are investigat ed by a combination of XPS and EELS techniques. As-prepared powder consists in particles with spinel structure and grain size of about 15 nm. Due to h igh reactivity towards oxygen of nanoparticules, a significant amount of Fe 2+ cations oxidize during precipitation, so that precipitated powders prese nt large deviation from oxygen-metal stoichiometry. Moreover precipitated p articles are evidenced to exhibit a strong surface titanium enrichment and an iron richer core. observation of such cation segregation proves that, du ring oxide formation process, kinetics of Ti precipitation is slower than t hat of Fe one. Conditions for tailoring nanocrystalline samples with satisf ying composition homogeneity are finally obtained by determination of an ap propriate annealing under oxidizing conditions which enables to eliminate F e-Ti segregation. (C) 1999 Published by Elsevier Science B.V. All rights re served.