Evolution of structural properties of iron oxide nano particles during temperature treatment from 250聽掳C-900聽掳C: X-ray diffraction and Fe K-shell pre-edge X-ray absorption study

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• 作者：Debajeet K. Bora^a ; ^b ; Artur Braun^a ; ^c ; ^{artur.braun@alumni.ethz.ch} ; Selma Erat^a ; ^d ; Olga Safonova^e ; Thomas Graule^a ; ^f ; Edwin C. Constable^b
• 关键词：Nano particle ; Iron oxide ; XANES ; Fe K-shell
• 刊名：Current Applied Physics
• 出版年：2012
• 期刊代码：15_15671739
• 类别：ph
• 出版时间：May, 2012
• 卷：12
• 期：3
• 页码：817-825
• 文件大小：1758 K

摘要

Iron oxide nano particles with nominal Fe₂O₃ stoichiometry were synthesized by a wet, soft chemical method with heat treatment temperatures from 250聽掳C to 900聽掳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聽nm to 150聽nm with increasing temperature. The mean primary particle size decreases from 105聽nm to 90聽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 t_2g/e_g 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聽掳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聽掳C showed that the nano particles have well developed lattice fringes corresponding to that of (110) plane of hematite.