Photoemission and Auger-electron spectroscopic study of the Chevrel-phase compound FexMo6S8.

Abstract

The electronic structure of the Chevrel-phase compound ${\mathrm{Fe}}_{\mathrm{x}}$${\mathrm{Mo}}_{6}$${\mathrm{S}}_{8}$ has been studied by photoemission and Auger-electron spectroscopy. Core-level shifts suggest a large charge transfer from the Fe atoms to the ${\mathrm{Mo}}_{6}$${\mathrm{S}}_{8}$ clusters and a small Mo-to-S charge transfer within the cluster. Line-shape asymmetry in the core levels indicates that the density of states (DOS) at the Fermi level has a finite S 3p component as well as the dominant Mo 3d character. Satellite structure and exchange splitting in the Fe core levels point to weak Fe 3d\char21{}S 3p hybridization in spite of the short Fe-S distances comparable to that in FeS. The x-ray and ultraviolet valence-band photoemission spectra and the Mo 4d partial DOS obtained by deconvoluting the Mo ${M}_{4}$,5VV Auger spectrum are compared with existing band-structure calculations, and the Mo 4d\char21{}S 3p bonding character, the structure of the Mo 4d-derived conduction band etc., are discussed. In particular, it is shown that the conduction-band structure is sensitive to the noncubic distortion of the crystal through changes in the intercluster Mo 4d\char21{}S 3p hybridization. A pronounced final-state effect is found in the Mo ${M}_{4}$,5${\mathrm{N}}_{2}$,3V Auger spectrum and is attributed to strong 4p-4d intershell coupling.