Crystal‐Field Splitting of Levels and X‐Ray Spectra of Transition Metal Monoxides

Abstract

The crystal-field splitting of the ground state of a transition metal ion in transition metal monoxides is calculated for the case of cubic symmetry. An investigation is made of the X-ray emission bands of metal and oxygen ions in the monoxides. The observed and calculated splittings of the levels are in good agreement.Es wird die Kristallfeldaufspaltung des Grundzustandes eines Ubergangsmetallions in Ubergangsmetallmonoxid fur den Fall kubischer Symmetrie berechnet. Die RontgenEmissionsbanden der Metall-und Sauerstoffionen in den Monoxiden werden untersucht. Die berechneten und beobachteten Aufspaltungen der Niveaus befinden sich in guter ubereinstimmung.At the present time calculations of the energy spectra by the method of augmented plane waves (APW) have the greatest value for understanding the electronic structure of solids and the interpretation of various spectra, especially X-ray spectra. This method enables one to estimate the relative position of bands of different symmetry, their width, and also, in the case of compounds, the fraction of charge located in spheres around each kind of atoms. However, APW calculations are rather complex and hardly accessible to experimenters. I n the range of the transition metal monoxides such calculations have only been performed for Ti0 and NiO [l, 21. Many details of the spectra can be explained by the simpler molecular-orbital and crystal-field methods. Although these methods deal with atomic levels and give only the magnitudes of splittings and not the band widths, this is in general sufficient for the interpretation of paramagnetic resonance, optical, and X-ray spectra.I n the present paper the crystal-field method is applied to estimating the splitting of the D and I? ground states of a transition metal ion having a partly filled 3d shell in a cubic crystal field, in the isostructural monoxides of the transition metals from Ti to Cu. It is assumed that the results of the calculations can be compared with the splittings observed experimentally in the shortwavelength K and L X-ray emission bands.The crystal-field splitting of the ground state for compounds having h'aC1 structure was calculated under the assumption of an average field by the L-S coupling method similarly as was done in [3] for spinels. It is well known that a fivefold degenerate d-level in a cubic field is split into threefold and twofold degenerate sublevels in an octahedral field which are given by