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The effect of valence state and site geometry on Ti L_3,2 and O K electron energy-loss spectra of Ti_xO_y phases

¹ Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Burgweg 11, D-07749 Jena, Germany
² Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany

Correspondence: ^* E-mail: emil.stoyanov{at}uni-bayreuth.de

Titanium L_3,2 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 L_3,2 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.

Key Words: Electron energy loss spectroscopy • valence state of titanium • titanium oxides • density functional theory