The electronic structure and the chemical bond in titanium dichalcogenides TiX₂ (X = S, Se, Te), which are promising electrode materials for lithium batteries, are studied experimentally and theoretically. It is found that the X-ray photoelectron spectra of the valence bands and the core levels of titanium and its X-ray L _{2, 3} absorption spectra demonstrate a change in the ionic and covalent components of the chemical bond in these compounds. The densities of states in these compounds are calculated by the full-potential augmented-plane-wave method, and multiplet calculations of the X-ray L _{2, 3} absorption spectra of titanium are performed. It is shown that, in the row TiS₂-TiSe₂-TiTe₂, the covalence increases, the ionicity of the chemical bond decreases, and the effect of the crystal field of a ligand is weakened.

The introduction of 3d transition metals into the van der Waals gaps of titanium dichalcogenides with layered structures gives rise to an interesting family of intercalation compounds, the physical properties of which differ substantially from those of the host compound due to “host–guest” and “guest–guest” interactions, resulting in ordering of the intercalated metal. Fe_xTiSe₂ is one of the most intriguing of such intercalation compounds due to its special electronic and magnetic properties. In this paper, the influence of the iron concentration on the crystal structure, electronic structure and chemical bond in the Fe_xTiSe₂ intercalation compounds is studied across a wide composition range (0 ≤ x ≤ 0.50) within the homogeneous region of the system. Photoelectron, resonance photoelectron and X-ray absorption spectroscopy methods were combined with thermodynamic electromotive force (EMF) measurements for the Li|Li⁺|Fe_xTiSe₂ cell in order to monitor the Fermi energy concentration dependence. The electronic structure changed substantially as the Fe content increased. A proposed model of the Fe_xTiSe₂ electronic structure transformation implies that iron atoms form Ti–Fe–Ti bonds at x < 0.40, but that Fe–Fe bonds prevail at x ≥ 0.40 when nanoscale iron chains appear in the van der Waals gap.

The probability of charge transfer in layered titanium diselenide between monolayers containing Cr, Mn, and Cu with different concentrations and host lattice TiSe₂ is estimated according to the resonant photoemission data. For this purpose, the Raman-Auger contributions and narrow bands just below the Fermi energy were separated in the valence band spectra. These contributions provide the information about charge transfer. It is shown that the localization of the 3d electrons is typical for Cr and Cu atoms and strongly depends on theirs concentration. In Mn_xTiSe₂, Mn 3d electrons are delocalized and the probability of the charge transfer is the greatest as compared with other compounds under investigation.