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

Abstract

We have conducted resonant angle-resolved photoemission spectroscopy of well-defined ${\mathrm{CeO}}_{2}$(111) and $c--{\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$(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 ${\mathrm{CeO}}_{2}$ is of a covalent nature, arising from hybridization with the $\mathrm{O}\phantom{\rule{0.16em}{0ex}}2p$ bands. In contrast, $c--{\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ exhibits an almost nondispersive $f$ state at 1.3 eV, which is indicative of almost negligible c-f hybridization.