X-ray Photoelectron Spectroscopy Study of Rare-Earth Filled Skutterudites LaFe4P12 and CeFe4P12

The electronic structure of the rare-earth filled skutterudites LaFe4P12 and CeFe4P12 was examined by high-resolution core-line and valence-band X-ray photoelectron spectroscopy (XPS). From analysis of the binding energies and line shapes in the core-line spectra, the formulations (La3+)(Fe2+)4(P-)12 and (Ce3+)(Fe2+)4(P-)12 were obtained, with the electron deficiency being represented by a hole in the valence band. The occurrence of trivalent cerium was confirmed by the presence of a partially filled 4f state found in the valence band spectrum of CeFe4P12 but not in LaFe4P12. The valence band spectra agree well with the density of states determined from band structure calculations. These spectra were fitted through a simple model in which component peaks are related to electron populations. Such an analysis gives atomic charges that are consistent with the formulations derived from the core-line spectra.