Phase decomposition study in COxFe3-xO4 iron cobaltites : Synthesis and structural characterization of the spinodal transformation

• Published in: Solid state sciences 2008-05, Vol.10 (5), p.550-556
• Main Authors: LE TRONG, H, BARNABE, A, PRESMANES, L, TAILHADES, Ph
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Material chemistry; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Phase diagrams of metals and alloys; Physics; Solubility, segregation, and mixing; phase separation
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2007.10.004

CoxFe3-xO4 iron cobaltites (1.21 < x < 2.35) have been prepared in the form of submicronic particles from mixed oxalic precursors heat treated at 900 and 600 deg C. The samples obtained at 900 deg C are made of a single spinel phase in which Co2+ and Fe3+ ions are distributed in both octahedral and tetrahedral sites and Co3+ ions are only located in the octahedral sublattice. For heat treatments carried out at 600 deg C two spinel phases are formed according to the phase diagrams. Pure Co1.7Fe1.3O4 oxide annealed at 700 deg C progressively transformed into two iron-rich and cobalt-rich spinel phases, respectively. More than 120 h of heat treatment is required to get the complete decomposition of the pristine oxide. At the beginning this oxide is submitted to a spinodal transformation. Alternating regions of iron-rich and cobalt-rich spinels are then created. The periodicity of the nanostructuration of the material is estimated to be close to 5 nm.