Electronic origin of ferroelectricity in multiferroic Lu0.5Sc0.5FeO3

We conducted a comprehensive study on the electronic structure of a multiferroic Lu0.5Sc0.5FeO3 single crystal using a range of techniques, including x-ray absorption spectroscopy, cluster model calculations, and ab initio analyses. Our x-ray linear dichroism measurements revealed strong hybridization of A-site d orbitals with neighboring O p orbitals. The hybridization strength of Lu 5d turns out to be not only much stronger but also more anisotropic than that of Sc 3d, leading to a huge ligand-field splitting between the out-of-plane a1g orbital state and in-plane egπ one. Based on our findings, we confirmed that Lu has a significantly larger ferroelectric energy gain compared to Sc. By combining our results with a simple phononic potential energy, we were able to quantify the ferroelectric energy landscape, which agrees well with the ab initio calculation result. Through a comparative analysis of Lu 5d and Sc 3d cases, we revalidate the rehybridization mechanism as the origin of ferroelectricity appearing in the h-A(Mn,Fe)O3 family.