Electronic Structure of NiAs-Type Transition-Metal Chalcogenides

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The purpose of this project is to show the x-ray K absorption spectra of 3d transition metals and its chalcogenides and oxides and the L_<II,III> absorption spectra of 4d transition-metal compounds and to obtain information on their electronic structures. The results are as following:A. The Co K absorption spectra of CoO and CoS are quite similar to each other and the Ni K absorption spectra of NiO and NiS are also similar to each other. B. The Co K absorption spectrum of CoSe is different from that of CoS (or CoO) but is similar to the K absorption spectrum of metallic cobalt. Such a result is found in the Ni K absorption spectra of nickel metal and its compounds. C. The Fe K absorption spectra of iron metal is similar to that of FeS.It is found that the p-like sates in the conduction bands of FeS, CoSe and NiSe are similar to those of metallic Fe, Co and Ni, respectively. The Fe, Co and Ni K absorption spectra of the chalcogenides and oxides are sensitive to the electronegativities of O, S, Se and Te.The subtle difference is found between the Nb L_<II,III> absorption spectra of Nb_2O_5 and NH_4NbF_6. Significant differences are also found between the Nb L_<II> and Nb L_<III> absorption spectra. These spectra are interpreted in terms of molecular-orbital theory.Sulfur K absorption spectra are calculated for NiAs type FeS, Cos and NiS crystals from a multiple-scattering approach within a muffin-tin-approximation.Cmparison between the calculated and experimental results indictes that a core hole created in the absorbing S atom does not so strongly affect the sulfur K absorption spectra of the metallic phase FeS, CoS and NiS.