Characterization of iron oxides by x-ray absorption at the oxygen K edgeusing a full multiple-scattering approach

Zhang, Wu; Gota, S.; Jollet, F.; Pollak, M.; Gautier-Soyer, M.; Natoli, C. R.

doi:10.1103/physrevb.55.2570

Cited by 222 publications

(232 citation statements)

References 27 publications

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“…12 At higher energies, the lineshape in the multiple scattering (MS) region is sensitive to atomic geometry through the impact of structure on the upper conduction band. 34,35 Although the spectra from the two phases are very similar, the exact position and strength of the MS resonance around 548 eV is diagnostic of the two phases (see asterisk in Fig. 5).…”

Section: Resultsmentioning

confidence: 99%

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

et al. 2010

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The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic-acidcoated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic-acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe Ledge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic-acid-coated sample. However, O K-edge absorption spectroscopy observed a ~0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase, and exert an effect on the global electronic and optical properties of the material.This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO 2 .

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Section: Resultsmentioning

confidence: 99%

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

et al. 2010

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“…The first structure (peak A in our case) is generally ascribed to the mixing between the transition metal d states with the O p states, thus giving information on the crystal field splitting of the 3d levels. In our data, this feature extends from 526 to 532 eV, and the fact that a single peak is observed suggests a very small crystal field splitting (a fit of this peak with two different Lorentzian functions yields a splitting lower than 0.5 eV between them [52], we note that this first structure appears always at approximately the same energies independently of the iron valence, in clear contradiction with the interpretation given by Ko et al [27], which implies the assignment of peaks A and B to the mixing of O p states with the Fe +3 and Fe +2 d states, respectively.…”

Section: Experimental and Calculation Detailsmentioning

confidence: 92%

Electronic states ofRFe2O4(R=Lu,Yb,Tm
Lafuerza
¹
,
García
²
,
Subı́as
³

et al. 2014
Phys. Rev. B
10
2
4
1
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We here report an investigation of the electronic states in the RFe 2 O 4 (R = Lu, Yb, Tm, Y) mixed-valence ferrites by means of soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements together with ab initio theoretical calculations. The presence of Fe +2 and Fe +3 pure ionic species is discarded in the XAS spectra at the O K edge in both experimental data and simulations based on the multiple scattering theory. Similarly, no trace of Fe +2 /Fe +3 contributions is detected in the XMCD spectra at the Fe K edge. On the other hand, the XAS and XMCD spectra at the Fe L 2,3 edges can be well described in terms of Fe +2 /Fe +3 contributions, and are also supported by multiplet calculations. This finding can be interpreted as the existence of a mixture of 3d 5 /3d 6 configurations at the Fe atoms. Alternative ferrimagnetic spin orderings based on a trimodal Fe valence distribution are also proposed and discussed. Finally, a possible explanation for the strong dependence of the Fe L 2,3 edges XMCD signal magnitude on both the sample surface preparation and detection method is presented.

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“…This effect is already visible in the case of MnTiO 3 where the pre-edge intensity is only 20% of the intensity of peaks ͑A͒ and ͑B͒. In addition, the O-K edge recorded in FeO in energy loss 48 or x-ray absorption 49 spectroscopies already show a low intensity of these 3d features with respect to the higher lying 4sp structures.…”

Section: The Unoccupied States Of Ilmenitesmentioning

confidence: 91%

High-resolution EELS investigation of the electronic structure of ilmenites

2006

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The electronic structure of a series of compounds belonging to the ilmenite family is investigated using high resolution electron energy loss spectroscopy ͑EELS͒. The energy loss near edge structure ͑ELNES͒ of the O-K, Ti-L 23 and transition metal L 23 edges have been recorded in MnTiO 3 , FeTiO 3 , CoTiO 3 , and NiTiO 3 with an energy resolution of 0.20-0.25 eV. The formal valency and spin-state of the transition metal are determined unambiguously from the analysis of the L 23 edges with theoretical ligand field multiplet calculations. The results confirm the evolution of the interatomic distances observed along this series. The O-K edge is analyzed by comparison to the experimental signatures observed in the structurally related Ti 2 O 3 compound and using theoretical molecular orbital results.

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Characterization of iron oxides by x-ray absorption at the oxygen K edgeusing a full multiple-scattering approach

Cited by 222 publications

References 27 publications

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Electronic states ofRFe2O4(R=Lu,Yb,Tm
Lafuerza
¹
,
García
²
,
Subı́as
³

et al. 2014
Phys. Rev. B
10
2
4
1
View full text Add to dashboard Cite

High-resolution EELS investigation of the electronic structure of ilmenites

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Characterization of iron oxides by x-ray absorption at the oxygen K edgeusing a full multiple-scattering approach

Cited by 222 publications

References 27 publications

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

Electronic states ofRFe2O4(R=Lu,Yb,TmLafuerza1, García2, Subı́as3 et al. 2014Phys. Rev. B10241View full textAdd to dashboardCite

High-resolution EELS investigation of the electronic structure of ilmenites

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Product

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About

Electronic states ofRFe2O4(R=Lu,Yb,Tm
Lafuerza
¹
,
García
²
,
Subı́as
³

et al. 2014
Phys. Rev. B
10
2
4
1
View full text Add to dashboard Cite