The effect of valence state and site geometry on Ti L3,2 and O K electron energy-loss spectra of TixOy phases

Titanium L3,2 and O K electron energy loss near-edge structures (ELNES) of seven Ti oxides have been measured in a transmission electron microscope to obtain information on the valence state and site geometry of Ti. The coordination of Ti in all phases studied is octahedral, whereas the valence states occurring are Ti2+, Ti3+, and Ti4+. Effects of polyhedra distortions are particularly observed for two oxides with mixed Ti3+-Ti4+ valence state, i.e., the Magnéli phases Ti4O7 and Ti5O9. A prominent pre-peak in the Ti L3 edge is attributed to the orthorhombic polyhedra distortions in these compounds, leading to complex crystal field splitting. The effect of valence state manifests itself in a systematic chemical shift of Ti white lines by 2 eV per valence state. On the basis of collected Ti L3,2 ELNES spectra we propose a new quantification technique for the determination of Ti4+/Ti3+ ratios. Complementary O K ELNES spectra were well reproduced by Density Functional Theory calculation, revealing that the O K-edge is sensitive to the covalent bonding in all analyzed oxides.