Valence state and electronic structure of the misfit-layer compound SmNbS3

Abstract

X-ray photoemission, X-ray absorption and reflection electron-energy-loss spectra of SmNbS3 have been measured for the first time. The results give no clear evidence for valence fluctuation or the occurrence of mixed-valence states for Sm atoms. The Sm 4d and 3d X-ray photoemission spectra suggest that Sm exists mainly as a trivalent ion like the pressure-induced metallic phase of SmS, in agreement with a recent lattice parameter measurement. The author has estimated that the number of Sm2+ ions is less than a few per cent of the number of Sm3+ ions, if they exist. Charge transfer from SmS layers to the incompletely filled Nb d(z2) band of NbS2 layers has an important effect on the valence state of Sm and the disappearance of a shoulder near the Nb L2 X-ray absorption edge. The Sm N4,5 inner-shell-electron-energy-loss spectrum exhibits non-optical transitions below the threshold, as has already been observed for the elemental metal Sm. The valence and conduction bands are also discussed.