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

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 i nvestigate the structure of the edge on the basis of trigonal (not octahedr al) coordination of the cation - especially the feature found at 13 eV abov e 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 da ta we show the p-d hybridisation and the creation of covalent bonding and d iscuss possible occurrence of many body effects which are responsible for M ott-Hubbard behaviour. (C) 1999 Elsevier Science S.A. All rights reserved.