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

The electronic structure of the rare-earth filled skutterudites LaFe 4 P 12 and CeFe 4 P 12 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 (La 3+ )(Fe 2+ ) 4 (P - ) 12 and (Ce 3+ )(Fe 2+ ) 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 CeFe 4 P 12 but not in LaFe 4 P 12 . 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.