X-ray-absorption spectra and electronic structures of vanadium dichalcogenides and their first-row transition-metal intercalates

The x-ray K absorption spectra of vanadium in vanadium dichalcogenides and in their first-row transition-metal intercalates M1/3VX₂ (M=V, Cr, Mn, Fe, Co, Ni; X=S, Se) have been measured together with those in V, V₂{O}₅$, and VSe, using a two-crystal spectrometer. The spectra of vanadium dichalcogenides and their first-row transition-metal intercalates have strong resemblance to each other and exhibit a weak flat structure followed by strong absorption. They reflect the transitions to the unoccupied vanadium d band with some p character and to the unoccupied vanadium 4s-4p bands, respectively. The midpoint of the initial rise of absorption is shifted to higher energies by intercalating the first-row transition metals. This shift is explained in terms of the charge-transfer model. It is, consequently, concluded that the rigid-band-model approach is valid as a first approximation at least for the unoccupied levels of these intercalation compounds.