Valence-band structure of the skutterudite compoundsCoAs3,CoSb3,andRhSb3studied by x-ray photoelectron spectroscopy
| Autor: | J.-P. Fleurial, H. Anno, Thierry Caillat, K. Matsubara |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Physical Review B. 62:10737-10743 |
| ISSN: | 1095-3795 0163-1829 |
| DOI: | 10.1103/physrevb.62.10737 |
| Popis: | The valence-band structure of ${\mathrm{CoAs}}_{3},$ ${\mathrm{CoSb}}_{3},$ and ${\mathrm{RhSb}}_{3}$ with a skutterudite-type crystal structure has been investigated by x-ray photoelectron spectroscopy. The photoemission spectra are compared with recent density-of-states calculations. Our photoemission spectra results and theoretical results are in good agreement for the energy positions in the metal d states and the pnicogen p states, but relatively large differences are found for the positions in the pnicogen s states. Based on our photoemission spectra, the electronic bonding states and the chemical trends are explained qualitatively in terms of a simple tight-binding model. The double localized and itinerant nature of the metal d states is also discussed in relation to the properties of the skutterudites. The metal d-derived density of states feature is clearly observed at about 1.2-, 1.4-, and 2.4-eV binding energies for ${\mathrm{CoSb}}_{3},$ ${\mathrm{CoAs}}_{3},$ and ${\mathrm{RhSb}}_{3},$ respectively. From the point of view of the crystal-field effects, it can be considered that this d-character band originates predominantly from the d orbitals with ${T}_{2g}$ symmetry, while d orbitals with ${E}_{g}$ symmetry hybridize strongly with the p orbitals forming the conduction band. Since the ${t}_{2g}$ states are considered to be almost completely filled, corresponding to the zero spin $S=0$ state ${(}^{1}{A}_{1},{t}_{2g}^{6}),$ most of skutterudites exhibit diamagnetic properties. On the other hand, the slight chemical shifts of the core levels as compared with the pure elements indicate a small charge transfer from metal to pnicogen atoms in the skutterudites, leading to hybridization between metal d states and pnicogen p states. p-d hybridization causes not only a substantial screening of atomic Coulomb interactions at metal sites, but also a strong covalent bonding in these materials. Concerning a particular point of the band structure in skutterudites, our photoemission spectra near the valence-band edge show clear experimental evidence of a small density of states around the Fermi level due to a single band crossing the pseudogap. |
| Databáze: | OpenAIRE |
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