Crystal-structure effects in the Ce L3-edge x-ray-absorption spectrum of CeO2: Multiple-scattering resonances and many-body final states.

Abstract

Here we report the interpretation of all spectral features of Ce ${\mathit{L}}_{3}$ x-ray-absorption near-edge structure (XANES) of ${\mathrm{CeO}}_{2}$ over a 40 eV range. The local partial unoccupied density of states in the initial state and in the fully relaxed final state have been calculated by the full multiple-scattering approach. The wave function of the excited electron in the final states of the Ce ${\mathit{L}}_{3}$-edge XANES spectrum is found to be determined by the multiple-scattering processes in a large size cluster formed by at least 45 atoms. We predict, in good agreement with the experimental data, the crystal-field splitting of 5d states in the final state ${\mathrm{\ensuremath{\Delta}}}_{\mathit{f}}$=4.0\ifmmode\pm\else\textpm\fi{}0.2 eV and its variation from the initial to the final state. The many-body final states for the 2p\ensuremath{\rightarrow}5,\ensuremath{\varepsilon}d transition, arising from the configuration interaction due to mixing of Ce 4f and O 2p valence orbitals, have been calculated taking into account the crystal-field splitting of the 5,\ensuremath{\varepsilon}d states and they give a full explanation for the low-energy shoulder on the Ce ${\mathit{L}}_{3}$ x-ray-absorption spectrum white line that was the object of a long-standing discussion. The origin of the pre-edge peak at about 10 eV below the white line maximum is explained as due to transitions at the bottom of the conduction band.