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

Abstract

The x-ray $K$ absorption spectra of vanadium in vanadium dichalcogenides and in their first-row transition-metal intercalates $M_{\frac{1}{3}}\mathrm{V}{X}_2$ ($M=\mathrm{V},\mathrm{ }\mathrm{C}\mathrm{r},\mathrm{ }\mathrm{M}\mathrm{n},\mathrm{ }\mathrm{F}\mathrm{e},\mathrm{ }\mathrm{C}\mathrm{o},\mathrm{ }\mathrm{Ni}$; $X=\mathrm{S},\mathrm{ }\mathrm{Se}$) have been measured together with those in V, ${\mathrm{V}}_2$ ${\mathrm{O}}_5$, 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.