Unified interpretation of pre-edge x-ray absorption fine structures in 3d transition metal compounds

Here we discuss origin of pre-edge features in the K-edge absorption spectra of transition metal atoms in octahedral coordination, in oxides and sulphides. We provide a unifying interpretation on the basis of multiple scattering simulations performed with different cluster models. We find that the pre-edge features arise due to hybridisation of the orbitals belonging to the central atom with the higher-shell metal orbitals. The results are obtained by performing multiple scattering simulations with cluster of size equal to the cation-cation plus the cation-anion bond lengths in order to ensure that the higher-shell metal atoms remain in the octahedral coordination. Within this framework, we are able to identify the electronic structure of the metal atoms and the ligand-field characters looking at position, shape and intensity of the different features observed in the XANES spectra.