Size-Dependent Phase Map and Phase Transformation Kinetics for Nanometric Iron(III) Oxides (γ → ε → α Pathway)

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• 作者：Seungyeol Lee ; Huifang Xu
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 23, 2016
• 年：2016
• 卷：120
• 期：24
• 页码：13316-13322
• 全文大小：725K
• 年卷期：0
• ISSN：1932-7455

文摘

Nanometric iron(III) oxide has been of great interest in a wide range of fields due to its magnetic properties, eminent biochemical characteristics, and potential for technological applications. Among iron oxides, ε-Fe₂O₃ is considered as a remarkable phase due to its giant coercive field at room temperature and ferromagnetic resonance capability. Here we present the first size-dependent phase map for ε-Fe₂O₃ via a γ → ε → α pathway together with the activation energies for the phase transformations, based on X-ray powder diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). HRTEM images of ε-Fe₂O₃ nanocrystals show both inversion and pseudohexagonal twins, which are fundamentally important for understanding the correlation between its nanostructure and magnetic properties. Two activation energies for γ-Fe₂O₃ → α-Fe₂O₃ phase transformations are 186.37 ± 9.89 and 174.58 ± 2.24 kJ mol^–1, respectively. The results provide useful information about the size, crystal structure, and transformation of the nanometric iron oxide polymorphs for applications in areas of developing engineered materials.