X-ray photoemission and Auger-electron spectroscopic study of the electronic structure of intercalation compounds MxTiS2 (M=Mn, Fe, Co, and Ni).

Abstract

The electronic structure of intercalation compounds ${M}_{x}$${\mathrm{TiS}}_{2}$ (M=Mn, Fe, Co, and Ni) has been studied by x-ray photoemission spectroscopy (XPS) and Auger-electron spectroscopy. The intercalated M 3d--derived spectra in the valence-band region can be interpreted in terms of multiplet and satellite structures, suggesting that the intra-atomic Coulomb and exchange energies for the M 3d electrons and the M 3d--S 3p hybridization dominate the M 3d-band width. The core-level XPS spectra of the guest 3d atoms also exhibit multiplet and satellite structures, from which these atoms are found to be in high-spin divalent states, except for Co, which is in the low-spin divalent state. The host Ti 3d-- and S 3p--derived electronic states, on the other hand, are basically well described by the band theory. Auger-electron spectra also support the strong electron correlation of the M 3d states and its insignificance for the host Ti 3d and S 3p states. Itinerant behaviors of the M 3d electrons as observed in the magnetic, thermal, and transport properties combined with the present results suggest that correlated M 3d bands are formed in these compounds as a result of strong hybridization with the host electronic states. The Ti 2p core-level XPS spectra of ${M}_{x}$${\mathrm{TiS}}_{2}$ are shown to consist of poorly screened and well-screened peaks. As for ${\mathrm{TiS}}_{2}$, the Ti 2p XPS spectrum does not show well-screened peaks because of the absence of conduction electrons that can fill the screening orbital, whereas this orbital appears to be filled in the initial state of Auger-electron emission.