Electronic structure of cage-like compound UB12 - Theory and XPS experiment

The electronic structure of cubic UB12 has been investigated by X-ray photoelectron spectroscopy (XPS) and first principles calculations employing the fully relativistic full-potential local-orbital (FPLO-9) method. The calculated densities of states (DOS) revealed unique fairly sharp five-peaks of the U 5f states with the lowest energy peak crossing the Fermi level. The calculated and experimental valence band XPS spectra are in very good accord, indicating a substantial delocalization of the U 5f electrons. On the other hand, our experimental U 4f core-level XPS spectrum exhibits both the 1-eV and 7-eV satellites, pointing to some localization effects of the U 5f electrons, which may exhibit a mixed-valence behavior. Our Fermi surfaces of UB12 calculated for ambient and such high pressure as 55 GPa show only negligible differences, which can explain the earlier reported stability of the cubic crystal structure of the studied system under high pressure.