showing 3 related works from this author
Mixed-Valence Defect Ferrites : a New Family of Fine Powders and Thin Films of Spinel Ferrites
1997
When highly divided spinel ferrites become reactive enough with oxygen, to allow the oxidation of the Fe 2+ ions at low temperature and of substitute cations too, when these cations are capable of different valence states. We prepared fine particles of spinel ferrites substituted by Mn, Mo, Cu, by chimie douce, especially from oxalate precursors and used them to reveal and to study the oxido-reduction phenomena occurring in these finely divided materials. It was shown that the oxidation created a new family of spinel ferrites : the mixed-valence defect ferrites, having specific characteristics and properties. The ferrites of this type can be fine powders prepared at low temperature, or grou…
Réactivité vis-à-vis de l'oxygène de spinelles de fer-vanadium de taille nanométrique et distribution cationique
1997
Resume L'etat de division des spinelles de fer-vanadium nanometriques V x Fe 3− x O 4 (0 ⩽ x ⩽ 2 ) permet d'oxyder au sein-meme de la structure spinelle les ions du fer et du vanadium. Les analyses calorimetriques et thermogravimetriques, ainsi que la spectroscopie infrarouge, montrent que les ions Fe B 2+ ,V B 3+ et Fe A 2+ sont oxydes successivement en ions Fe 3+ et V 5+ a des temperatures inferieures a 450 °C. Les spinelles lacunaires a valence mixte qui en resultent, ont un taux en lacunes croissant avec x, qui peut etre superieur a ceux determines jusqu'alors pour ce type d'oxydes.
Temperature dependence of oxidation behavior and coercivity evolution in fine-grained spinel ferrites
2000
Abstract The present paper reviews for a series of fine-grained MxCoyFe(3−x−y)O4 spinel ferrites (M=Mn, Mo, Cu, V) which oxidize into mixed-valence defect ferrites, a systematic study of the correlation between the oxidation temperature and the variation of coercivity. An increase of the coercivity is observed as often as the oxidation reactions Fe2+→Fe3+ and Mn+→M(n+m)+ (1⩽m⩽3) occur. This enhancement of coercivity has been explained by stresses generated during each specific oxidation reaction. The well-known property of cobalt to strongly magnify the magnetostrictive effects has been used to support this interpretation.