Fock, J;
Bogart, LK;
Gonzalez-Alonso, D;
Espeso, JI;
Hansen, MF;
Varon, M;
Frandsen, C;
(2017)
On the 'centre of gravity' method for measuring the composition of magnetite/maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via Fe-57 Mossbauer spectroscopy.
Journal of Physics D: Applied Physics
, 50
(26)
10.1088/1361-6463/aa73fa.
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Abstract
We evaluate the application of 57Fe Mössbauer spectroscopy to the determination of the composition of magnetite (Fe3O4)/maghemite (γ-Fe2O3) mixtures and the stoichiometry of magnetite-maghemite solid solutions. In particular, we consider a recently proposed model-independent method which does not rely on a priori assumptions regarding the nature of the sample, other than that it is free of other Fe-containing phases. In it a single parameter, δRT—the ‘centre of gravity’, or area weighted mean isomer shift at room temperature, T = 295 ± 5 K—is extracted by curve-fitting a sample’s Mössbauer spectrum, and is correlated to the sample’s composition or stoichiometry. We present data on highpurity magnetite and maghemite powders, and mixtures thereof, as well as comparison literature data from nanoparticulate mixtures and solid solutions, to show that a linear correlation exists between δRT and the numerical proportion of Fe atoms in the magnetite environment: α = Femagnetite/Fetotal = − ( ) δ δ RT o /m, where δo = 0.3206 ± 0.0022mm s−1 and m = 0.2135 ± 0.0076mm s−1 . We also present equations to relate α to the weight percentage w of magnetite in mixed phases, and the magnetite stoichiometry x = Fe2+/Fe3+ in solid solutions. The analytical method is generally applicable, but is most accurate when the absorption profiles are sharp; in some samples this may require spectra to be recorded at reduced temperatures. We consider such cases and provide equations to relate δ ( ) T to the corresponding α value.
| Type: | Article |
|---|---|
| Title: | On the 'centre of gravity' method for measuring the composition of magnetite/maghemite mixtures, or the stoichiometry of magnetite-maghemite solid solutions, via Fe-57 Mossbauer spectroscopy |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1088/1361-6463/aa73fa |
| Publisher version: | http://doi.org/10.1088/1361-6463/aa73fa |
| Language: | English |
| Additional information: | © 2017 IOP Publishing Ltd. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. |
| Keywords: | Science & Technology, Physical Sciences, Physics, Applied, Physics, magnetite, maghemite, composition of mixtures, stoichiometry of solid solutions, Mossbauer spectroscopy, VERWEY TRANSITION, CORROSION BEHAVIOR, SINGLE-CRYSTAL, IRON-OXIDES, X-RAY, NANOPARTICLES, PALEOINTENSITY, DIFFRACTION, DISSOLUTION, GAMMA-FE2O3 |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1567594 |
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