X-ray photoelectron spectroscopy study of the skutteruditesLaFe4Sb12,Ce

Abstract

The electronic structure of the skutterudites CoSb 3 , CoP 3 , LaFe 4 Sb 12 , and CeFe 4 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 CoSb 3 and CoP 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 LaFe 4 Sb 12 but not in LaFe 4 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 CeFe 4 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 ͑Co 3+ ͒͑Pn 1− ͒ 3 and ͑R 3+ ͒͑Fe 2+ ͒ 4 ͑Sb 1− ͒ 12 , with the electron deficiency in the rare-earth containing compounds being represented by a hole in the valence band.

Examination of CeFe4Sb12 upon exposure to air: Is this material appropriate for use in terrestrial, high-temperature thermoelectric devices?

“…For comparison, spectra from Fe 2 O 3 and FeSbO 4 are shown in the inset. The spectrum from as-synthesized CeFe 4 Sb 12 is comprised of 3 main excitations and corresponds to low-spin Fe 2+ , an electronic state that has been proven by previous studies [18,22]. The lowest energy peak in the spectrum (∼7114 eV) represents a pre-edge, Fe 1s → Fe 3d, excitation.…”

“…The purity of the synthesized materials was confirmed by powder X-ray diffraction (pXRD) using a Rigaku Rotaflex RU-200 rotating anode X-ray diffractometer. FeSbO4 was phase-pure while CeFe4Sb12 was found to contain a minor concentration of the commonly observed impurity, FeSb2 [12,18].…”

Stability and electronic structure of the Co–P compounds from first-principle calculations

“…Due to excellent properties of Co-P compounds, the synthesis technologies have been extensively investigated [16][17][18] and the structural analysis has also been conducted in order to understand the intrinsic mechanism [19][20][21][22][23]. By the linear muffin-tin orbital method in the atomic sphere approximation (LMTO-ASA), it has been found that Co 2 P with hexagonal structure exhibits ferromagnetism while Co 2 P with orthorhombic structure reveals non-magnetic character [19].…”

An XPS study of the interatomic charge distribution in stainless steels

“…In another study on Co-based compounds, [10] the ionic character of the Co-P bond in CoP 3 was further supported by monitoring the intensity of the Co 2p energy loss peak. The observed reduction of the intensity of the loss feature in CoP 3 compared to pure Co was interpreted as a reduction of the Co valence electrons.…”