Covalent versus localized nature of 4 f electrons in ceria: Resonant angle-resolved photoemission spectroscopy and density functional theory

We have conducted resonant angle-resolved photoemission spectroscopy of well-defined CeO2(111) and c-Ce2O3(111) model surfaces, revealing distinct f contributions in the valence band of the two compounds. In conjunction with density functional theory calculations, we show that the f contribution in CeO2 is of a covalent nature, arising from hybridization with the O 2p bands. In contrast, c-Ce2O3 exhibits an almost nondispersive f state at 1.3 eV, which is indicative of almost negligible c-f hybridization.