The cationic composition of a titanium ferrite
(Fe2.5Ti0.5O4) has been followed by XPS
during its oxidation in cation deficient phases
(without crystallographic transformation) in
order to reveal a dynamic segregation
phenomenon. Indeed, during this oxidation, an
important modification of the chemical
composition of the first layers of the material has been
revealed: below 350 °C, the titanium
ferrites surface becomes richer in iron and poorer in
titanium. But, if the reaction is
extended above 400 °C, some 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 present
in the material. Finally, at 450 °C, on the surface of the
spinel, the α–Fe2O3
phase begins to appear and hides the ferrite.