Evolution of structural properties of iron oxide nano particles during temperature treatment from 250 °C-900 °C: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study |
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Authors: | Debajeet K Bora Artur Braun Selma Erat Olga SafonovaThomas Graule Edwin C Constable |
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Institution: | a Laboratory for High Performance Ceramics, Empa, Swiss Federal Laboratories for Material Science and Technology, CH-8600 Dübendorf, Switzerland b Department of Chemistry, University of Basel, CH-4056 Basel, Switzerland c Hawaii Natural Energy Institute, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, Honolulu, HI 96822, USA d Department of Nonmetallic Inorganic Materials, ETH Zürich-Swiss Federal Institute of Technology, CH-8037 Zürich, Switzerland e Swiss Norwegian Beamline, European Synchrotron Radiation Facility (ESRF), Grenoble-38043, France f Technische Universität Bergakademie Freiberg, D-09596 Freiberg, Germany |
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Abstract: | Iron oxide nano particles with nominal Fe2O3 stoichiometry were synthesized by a wet, soft chemical method with heat treatment temperatures from 250 °C to 900 °C in air. The variation in the structural properties of the nano particles with the heat treatment temperature was studied by X-ray diffraction and Fe K-shell X -ray absorption spectroscopy. X-ray diffractograms show that at lower annealing temperatures the nano particle comprise both maghemite and hematite phases. With increasing temperature, the remainder of the maghemite phase transforms completely to hematite. Profile analysis of the leading Bragg reflections reveals that the average crystallite size increases from 50 nm to 150 nm with increasing temperature. The mean primary particle size decreases from 105 nm to 90 nm with increasing heat treatment temperature. The X-ray diffraction results are paralleled by systematic changes in the pre-edge structure of the Fe K-edge X-ray absorption spectra, in particular by a gradual decrease of the t2g/eg peak height ratio of the two leading pre-edge resonances, confirming oxidation of the Fe from Fe2+ towards Fe3+. Transmission electron microscopy (TEM) on the samples treated at temperatures as high as 900 °C showed particles with prismatic morphology along with the formation of stacking fault like defects. High resolution TEM with selected area electron diffraction (SAED) of samples heat treated above 350 °C showed that the nano particles have well developed lattice fringes corresponding to that of (110) plane of hematite. |
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Keywords: | Nano particle Iron oxide XANES Fe K-shell |
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