Effect of surface macrodefects on the mechanism of oxygen interaction with the boundary layer of Fe2O3

The interaction between gaseous oxygen and the surface of sintered polycrystalline Fe₂O₃ was studied by using “in situ” work function measurements at 1140 K (867°C). The treatment of the specimen (after preliminary sintering at 1673 K in air) involved polishing of the oxide surface with a diamond powder resulting in the formation of a high density of grooves of different orientations along the surface. Sorption of oxygen on the freshly polished surface resulted in the formation of a positive surface charge which has been considered in terms of the formation of subsurface microdipoles, induced either by specific active centres formed during the mechanical treatment, or by donors formed at the same centres. The centres were closely related to the presence of grooves. The charge decreased during the thermal treatment and finally changed in sign. It was also observed that the treatment led to disappearance of grooves except some with specific orientation. The time of the equilibration, whose rate is controlled by the surface diffusion, was about 300 h at 1140 K.