A photoemission study of Sb-doped TiO2

The influence of Sb-doping on the electronic structure of TiO2 (rutile) has been investigated by core and valence level photoemission spectroscopy, supplemented by high resolution electron microscopy, SQUID magnetometry and infrared reflectance spectroscopy. Pronounced segregation of Sb to polycrystalline TiO2 surfaces is evident from core level XPS, with a surface Sb concentration that increases only weakly with nominal Sb doping level in the range between 1% and 10%. Segregated Sb ions may be imaged directly in high resolution transmission electron microscopy. Ultraviolet photoemission spectra reveal the presence of an Sb-induced state toward the bottom of the bulk bandgap. The experimental data are discussed in terms of a model involving bulk substitution of Sb(V) ions onto Ti(IV) sites, largely compensated by cation vacancies or anion interstitials. Electrons are trapped by surface Sb ions to generate an Sb(III) lone-pair-like surface state. The influence of Sb doping on the electronic structure of TiO2 is contrasted with the behaviour of Sb in SnO2.