Fe valence state of Sr2FeMoO6 probed by x-ray absorption spectroscopy: The sample age matters

Kuepper, K.; Raekers, Michael; Taubitz, Christian; Hesse, H.; Neumann, M.; Young, A. T.; Bondino, Federica

doi:10.1063/1.2955749

Cited by 19 publications

(17 citation statements)

References 26 publications

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“…Such extremely small changes of entropy, as well as small temperature intervals of phase transformations (within 20 K), are caused by impurity phases distributed as inclusions in the basic, double perovskite matrix and magnetic phase transitions in local areas. The occurrence of this phase transition at 188 K in SFMO-6 and SFMO-9 powders could be related to the paramagnetic–antiferromagnetic, magnetic phase transition in the wustite (Fe 0.947 O) [20–22]. This indicates the non-single-phase nature of the SFMO-6 and SFMO-9 samples.…”

Section: Resultsmentioning

confidence: 95%

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6−x nanopowders formed by the citrate–gel method

Yarmolich¹,

Каланда²,

Demyanov³

et al. 2016

Beilstein J. Nanotechnol.

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SummaryThe sequence of phase transformations during Sr2FeMoO6−x crystallization by the citrate–gel method was studied for powders synthesized with initial reagent solutions with pH values of 4, 6 and 9. Scanning electron microscopy revealed that the as-produced and annealed powders had the largest Sr2FeMoO6−x agglomerates with diameters in the range of 0.7–1.2 µm. The average grain size of the powders in the dispersion grows from 250 to 550 nm with increasing pH value. The X-ray diffraction analysis of the powders annealed at different temperatures between 770 and 1270 K showed that the composition of the initially formed Sr2FeMoO6−x changes and the molybdenum content increases with further heating. This leads to a change in the Sr2FeMoO6−x crystal lattice parameters and a contraction of the cell volume. An optimized synthesis procedure based on an initial solution of pH 4 allowed a single-phase Sr2FeMoO6−x compound to be obtained with a grain size in the range of 50–120 nm and a superstructural ordering of iron and molybdenum cations of 88%.

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Section: Resultsmentioning

confidence: 95%

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6−x nanopowders formed by the citrate–gel method

Yarmolich¹,

Каланда²,

Demyanov³

et al. 2016

Beilstein J. Nanotechnol.

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“…39 The iron TEY spectrum from OA-coated nanoparticles indicates the surface to be composed of maghemite, but the FY signal reveals a different spectrum originating from the interior (Fig. 6).…”

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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“…All spectra collected were calibrated, normalized, and analyzed using the Athena software program [51]. As Sr 2 FeMoO 6 materials have been shown to degrade into SrMoO 4 and other products over time, to eliminate the possibility of sample age significantly affecting the collected spectra, all spectra were collected within one month of sample preparation [52].…”

Section: Xanesmentioning

confidence: 99%

An investigation of the Fe and Mo oxidation states in Sr2Fe2−xMoxO6 (0.25⩽x⩽1.0) double perovskites by X-ray absorption spectroscopy

Hayes

Grosvenor

2012

Journal of Alloys and Compounds

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Fe valence state of Sr2FeMoO6 probed by x-ray absorption spectroscopy: The sample age matters

Cited by 19 publications

References 26 publications

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6−x nanopowders formed by the citrate–gel method

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6−x nanopowders formed by the citrate–gel method

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

An investigation of the Fe and Mo oxidation states in Sr2Fe2−xMoxO6 (0.25⩽x⩽1.0) double perovskites by X-ray absorption spectroscopy

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Fe valence state of Sr2FeMoO6 probed by x-ray absorption spectroscopy: The sample age matters

Cited by 19 publications

References 26 publications

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr2FeMoO6−x nanopowders formed by the citrate–gel method

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr2FeMoO6−x nanopowders formed by the citrate–gel method

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

An investigation of the Fe and Mo oxidation states in Sr2Fe2−xMoxO6 (0.25⩽x⩽1.0) double perovskites by X-ray absorption spectroscopy

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Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6−x nanopowders formed by the citrate–gel method

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr₂FeMoO_6−x nanopowders formed by the citrate–gel method