Speculations on anomalous chemical states of Ti ions in FeTiO3 observed by high-resolution X-ray Kβ emission spectra

Graphical abstract: Display Omitted Research highlights: → High-resolution Ti Kβ emission spectra of MTiO3 (M = Ti, Mn, Fe, Co, or Ni) compounds. → Origin of anomalous valence states of Ti ions in FeTiO3 observed by XES. → Theoretical Ti Kβ spectra assuming the [Ti3+O6]9- or [Ti4+O6]8- cluster. → M2+→Ti4+ inter-valence charge transfer induced by the core-hole states. -- Abstract: A series of high-resolution Ti Kβ X-ray emission spectra were measured for various isomorphous titanium oxides with composition MTiO3, where M was divalent Mg, Mn, Fe, Co, or Ni. The detailed spectral features of Ti Kβ lines for MTiO3 were intermediate between those of TiO2 and Ti2O3 depending on the coexisting cation species M, though the formal valence states of all Ti ions in MTiO3 were consistent with those in TiO2. Especially in the case of FeTiO3, the features in both main and satellite lines had many similarities of Ti2O3. The Ti Kβ X-rays of FeTiO3 seemed to be emitted by the transition from Ti3+-like states. Because of the small difference in energies and the large overlap between Ti 3d and Fe 3d orbitals, intermediate core-hole states occurring on the X-ray emission process might produce the inter-valence charge transfer from Fe2+ to Ti4+ to form the Ti3+-like states. The DV Xα calculations based on the molecular orbital theory can reproduce the satellite structures to assume the increasing 3d electron densities on Ti for FeTiO3.