Electronic structure of Ni_xTiSe₂ (0.05 ≤ x ≤ 0.46) compounds with ordered and disordered Ni

The electronic structure of the Ni_xTiSe₂ intercalation compounds with disordered and ordered Ni atoms is studied using photoelectron, resonant photoelectron and X-ray absorption spectroscopy, theoretical calculations of the X-ray spectra and density of electronic states. The increase in the covalent component of the chemical bond of Ni and Ti with the nearest neighbour was found with increasing nickel concentration and its ordering. A significant charge transfer from the Ni atoms to the host lattice resulting in the transformation of Ti⁴⁺ into Ti³⁺ occurs, while the symmetry of the crystal lattice is lowered from the hexagonal to the monoclinic one.