X-ray photoelectron spectroscopy study of the skutterudites LaFe4Sb12, CeFe4Sb12, CoSb3, and CoP3

Abstract

The electronic structure of the skutterudites $\mathrm{Co}{\mathrm{Sb}}_3$, $\mathrm{Co}{\mathrm{P}}_3$, $\mathrm{La}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$, and $\mathrm{Ce}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ has been investigated with x-ray photoelectron spectroscopy. The binding energies in the pnicogen and transition metal $2p$ spectra are shifted to reflect changes in the bonding character of these compounds. The asymmetric line shapes in the metal $2p$ spectra signal electronic delocalization. A plasmon loss satellite peak occurs in the Co $2p$ spectra of $\mathrm{Co}{\mathrm{Sb}}_3$ and $\mathrm{Co}{\mathrm{P}}_3$. The intensity of this peak in these and other Co-containing compounds increases with greater occupancy of the Co $3d$ band. The presence of trivalent rare earth was confirmed from the La and Ce $3d$ spectra, both of which contain shake-up satellite peaks. A second satellite peak, attributable to two-core-hole processes, also appears in the La $3d$ spectrum of $\mathrm{La}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ but not in $\mathrm{La}{\mathrm{Fe}}_4{\mathrm{P}}_{12}$, indicating the involvement of La-Sb covalent bonding and the population of La $4f$ conduction states in the former. This peak is absent in the Ce $3d$ spectrum of $\mathrm{Ce}{\mathrm{Fe}}_4{\mathrm{Sb}}_{12}$ because a $4f^1$ state is located below the Fermi edge. Fitting of the valence band spectra for all four compounds led to the formulations $\left({\mathrm{Co}}^{3+}\right){\left(P{n}^{1-}\right)}_3$ and $\left(R^{3+}\right){\left({\mathrm{Fe}}^{2+}\right)}_4{\left({\mathrm{Sb}}^{1-}\right)}_{12}$, with the electron deficiency in the rare-earth containing compounds being represented by a hole in the valence band.