An Anomalous Electron Configuration Among 3d Transition Metal Atoms

Physical properties of materials are mainly determined by valence electron configurations, where different valence shells would induce divergent phenomena. In compounds containing Sc2+, 3d electron occupancy is expected, the same as other transition metal atoms like Ti3+. But this situation still awaits experimental verification in inorganic materials. Here, we selected ScS to measure the valence electron density and orbital population of Sc2+ through delicate quantitative convergent-beam electron diffraction. With the absence of 3d orbital features around Sc-atom sites and the nearly bare population of t(2g) orbital, the unintuitive occupation of 4s orbital in Sc2+ is concluded. It should be the first time to report such a special electron configuration in a transition metal compound, in which 4s rather than 3d orbital is preferred. Our findings reveal the distinct behavior of Sc and probable ways to modulate material properties by controlling electron orbitals.

Automated summary

The physical properties of materials are determined by the valence electron configurations, and different valence shells lead to different phenomena. In this study, we examined the valence electron density and orbital population of Sc2+ in the compound ScS using quantitative convergent-beam electron diffraction. Our results show that the 4s orbital is occupied by Sc2+, which is unexpected as it is usually the 3d orbital that is occupied in transition metal atoms. This finding reveals a unique electron configuration in a transition metal compound and suggests potential ways to modulate material properties by controlling electron orbitals.