Surface composition analysis during the oxidation of ferrites: A necessity

The cationic composition of a titanium ferrite (Fe2.5Ti0.5O4) has been foll owed by XPS during its oxidation in cation deficient phases (without crysta llographic transformation) in order to reveal a dynamic segregation phenome non. Indeed, during this oxidation, an important modification of the chemic al composition of the first layers of the material has been revealed: below 350 degrees C; the titanium ferrites surface becomes richer in iron and po orer in titanium. But, if the reaction is extended above 400 degrees C; som e titanium can move to the surface. This phenomenon has been interpreted on the basis of the differences of mobility of the different ions which are p resent in the material. Finally, at 450 degrees C, on the surface of the sp inel, the alpha-Fe2O3 phase begins to appear and hides the ferrite.