Chemical bonds in intercalation compounds Cu_xTiCh₂ (Ch = S, Te)

A thorough study of the chemical bonding between intercalated copper and host lattice TiCh₂ (Ch = S, Te) was performed. In order to separate the contributions of the copper, titanium, and chalcogen states into the electronic structure of the valence band, photoelectron spectroscopy in nonresonant and resonant (Cu 3p-3d and Ti 2p-3d) excitation modes was used. It is shown that the ionicity of the chemical bond between copper and host lattice is decreased in the TiS₂ → TiSe₂ → TiTe₂ row. In Cu_xTiS₂, copper atoms form the chemical bond with TiCh₂ host lattice, while in Cu_xTiTe₂ directly with tellurium atoms.