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Caliebe, W.; Kao, C.‐C.; Hastings, J. B.; Taguchi, M.; Kotani, Akio; Uozumi, Takayuki; Groot, Frank M. F. de

doi:10.1103/physrevb.58.13452

Cited by 71 publications

(50 citation statements)

References 32 publications

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“…By detecting the K intensity as a function of the incident energy it is thus possible to record absorptionlike spectra. [25][26][27] The advantage of high-resolution K -detected XANES spectroscopy is that it shows spectral features that are sharper than in conventional absorption spectroscopy recorded in transmission mode or by fluorescence detection using a solidstate detector with medium energy resolution (e.g., Ge: ∆E ∼ 200 eV). We show that high-resolution K -detected XANES spectra allow for a more precise background subtraction and consequently a higher accuracy in determining the local geometry and oxidation state of Fe in ZSM-5.…”

Section: Introductionmentioning

confidence: 99%

Kβ-Detected XANES of Framework-Substituted FeZSM-5 Zeolites

et al. 2004

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The valence and local symmetry of iron in framework-substituted FeZSM-5 with a high Fe dilution (Si/Fe ) 360) was studied by means of K -detected X-ray absorption spectroscopy. This technique combines highresolution (∆E ∼1 eV) fluorescence detection of the 3p to 1s (K ) transition with the X-ray absorption near-edge structure (XANES) at the Fe K-edge. An absorption-like spectrum is recorded by detecting the K fluorescence intensity as a function of the incident energy that is scanned through the K absorption edge. K -detected XANES spectra allow for a more precise separation of the weak K pre-edge structure from the main edge as compared to conventional absorption spectroscopy. Subsequent analysis and interpretation of the pre-edge spectral features therefore is more accurate. The pre-edge is sensitive to changes in the local coordination and oxidation state of Fe. Using this technique we were able to quantitatively determine the degree of iron extraction out of a zeolite framework upon steaming. With the use of appropriate reference compounds, the pre-edge analysis was used to monitor the activation of low-loaded, framework-substituted FeZSM-5 (0.3 wt % Fe). Template removal and calcination distort the zeolite framework and induce a deviation from T d symmetry for incorporated iron. The (deliberate) presence of water at high temperature (T > 500°C) facilitates the hydrolysis of the Si-O-Fe bonds and increases the formation of extraframework iron species. The amount of Fe III occupying tetrahedral sites in the MFI-type zeolite decreases to 32% and 19%, respectively, for mild-and hard-steamed samples.

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Section: Introductionmentioning

confidence: 99%

Kβ-Detected XANES of Framework-Substituted FeZSM-5 Zeolites

et al. 2004

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“…In this regard, the evolution of the Fe 3d electronic structure vs pressure can be investigated from the pre-edge region of the Fe K-edge absorption spectrum (top panel of Fig. 3), since this preedge feature can be assigned to transitions to the t2g and eg components of the 3d band [11,32] and, therefore, is directly connected to the population of the HS and LS states. After normalization and background subtraction of absorption spectra (top panel of Fig.…”

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confidence: 99%

Local structure and spin transition inFe2O3hematite at high pressure

et al. 2016

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The pressure evolution of the local structure of Fe2O3 hematite has been determined for the first time by extended x-ray absorption fine structure up to ∼79 GPa. The comparison to the different high-pressure forms proposed in the literature suggests that the orthorhombic structure with space group Aba2 is the most probable. The crossover from Fe high-spin to low-spin states with pressure increase has been monitored from the pre-edge region of the Fe K-edge absorption spectra. The "simultaneous" comparison with the local structural changes allows us to definitively conclude that it is the electronic transition that drives the structural transition and not viceversa.The high-pressure behavior of hematite (α-Fe 2 O 3 ) has raised much debate in the scientific community over the past decades. At ambient conditions, hematite crystallizes in the rhombohedral corundum-type structure, space group R3c, and is a wide-band antiferromagnetic insulator. By increasing pressure at room temperature, the corundum structure of hematite is progressively distorted and, above ∼50 GPa, a series of physical changes occur [1][2][3][4][5][6][7][8][9][10][11]: the unit cell volume drops down by about 10 %, the crystal symmetry changes completely, the electrical resistivity decreases drastically due to the breakdown of the d-electron correlation (Mott insulator-metal transition), the magnetic moments collapse [transition of iron ions from high-spin (HS) to low-spin (LS) state] and the long-range magnetic order disappears. Besides being interesting from the viewpoint of solid-state physics, the phenomena are also important in geophysics for modeling materials behavior in deep Earth's mantle [12][13][14][15][16].

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“…The quadrupole contributions were calculated using the multiplet code with the same parameters as presented in Table I. The dipolar part was modeled using a phenomenological density of p symmetry final states similar to the model used by Caliebe et al 49 in calculating the pre-edge of Fe K-absorption edge of Fe 2 O 3 . The charge transfer multiplet calculation predicts a single peak in the pre-edge for the LS state, which originates from transitions into e g levels.…”

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confidence: 99%

Temperature- and pressure-induced spin-state transitions inLaCoO3

et al. 2006

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We report the continuous variation of the spin moment of cobalt in LaCoO3 across its temperature and pressure-induced spin transitions evidenced with Kβ emission spectra. The first thermal transition is best described by a transition to an orbitally nondegenerate intermediate spin (S=1) state. In parallel, continuous redistribution of the 3d electrons is also indicated by partial fluorescence yield X-ray absorption spectra. At high pressure, our study confirms that the material becomes low spin between 40 and 70 kbar at room temperature.

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1s2presonant inelastic x-ray scattering inα−Fe2O

Cited by 71 publications

References 32 publications

Kβ-Detected XANES of Framework-Substituted FeZSM-5 Zeolites

Kβ-Detected XANES of Framework-Substituted FeZSM-5 Zeolites

Local structure and spin transition inFe2O3hematite at high pressure

Temperature- and pressure-induced spin-state transitions inLaCoO3

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