Effect of oxygen activity on niobium segregation in niobium-doped titanium dioxide

The present paper considers the effect of segregation of niobium in polycrystalline, Nb-doped titanium dioxide, Nb-TiO2. Specifically, the effect of oxygen activity, controlled during processing, on segregation is investigated. It was observed that Nb segregation is favoured by low oxygen activity, especially when the Nb dopant concentration is less than 3 at %. This is interpreted in terms of the defect equilibria that describe Nb incorporation. While it is not considered that the present data reflect equilibrium segregation, it is considered that the observed behaviour is tending towards the equilibrium case, and so the applied interpretation is valid. From these results it is clear that segregation may be controlled in order to impose desired functional properties in advanced materials such as TiO2 for solar driven water splitting.