Iron(II) cobalt ferrites. Preparation and interfacial behaviour

Relations between the interfacial and the chemical-structural features of oxides are of concern in several fields. Ferrites appear as a particularly suitable system as they allow gradual changes in composition while avoiding complications from structural modifications. A family of iron(II) cobalt ferrites (CoxFe3-xO4, 0.25 < x < 1) was prepared by a wet procedure and characterized for phase purity and cationic Co/Fe composition. Auger surface analyses showed that the Co/Fe ratio does not undergo significant modifications in passing from the bulk to the surface. Parameters of the electrical double layer (pHp.z.e. and isoelectric point) have been determined for all the oxide compositions. Results show that the pHp.z.e. and isoelectric point values vary as a continuous function of the degree of substitution of Co for Fe.