XANES study of sulphur K edges of transition metal (V, Cr, Mn, Fe, Co, Ni) monosulphides: experiment and LMTO numerical calculations

Abstract

In our study we investigate the anion X-ray absorption edges of transition metal (TM) monosulphides. The compounds VS, CrS, FeS, CoS, NiS possess NiAs structure, whilst MnS has the NaCl structure. For hexagonal compounds we investigate the structure of the edge on the basis of trigonal (not octahedral) coordination of the cation – especially the feature found at 13 eV above the edge. We argue that the occurrence of this peak in FeS, CoS, NiS and absence in VS, CrS, may be caused by Mott–Hubbard transition and therefore we assign it to the upper Hubbard portion of the hybridised Fe d–S p level. We discuss this effect on the basis of the molecular orbital (MO) model as well as LMTO (linear muffin tin orbital) calculations. In our numerical data we show the p–d hybridisation and the creation of covalent bonding and discuss possible occurrence of many body effects which are responsible for Mott–Hubbard behaviour.