Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
J Am Chem Soc. 2009 Dec 30;131(51):18299-303. doi: 10.1021/ja9046069.
Iron oxide (Fe(2)O(3)) has four crystal structures: gamma-, epsilon-, beta-, and alpha-Fe(2)O(3). Until now, routes of the phase transformations among the four Fe(2)O(3) phases have not been clarified because a systematic synthesis that yields all four Fe(2)O(3) phases has yet to be reported. Herein we report the synthesis of a series of Fe(2)O(3) nanoparticles using mesoporous SiO(2). The crystal structures of the Fe(2)O(3) nanoparticles change in the order of gamma-Fe(2)O(3) --> epsilon-Fe(2)O(3) --> beta-Fe(2)O(3) --> alpha-Fe(2)O(3) as the particle size increases. Threshold sizes were estimated as gamma --> epsilon at 8 nm, epsilon --> beta at 30 nm, and beta --> alpha at 50 nm in the synthesis using FeSO(4) as a precursor. The phase transformations among the four Fe(2)O(3) phases have been observed for the first time.
四氧化三铁（Fe2O3）有四种晶体结构：γ-、ε-、β-和α-Fe2O3。到目前为止，四种 Fe2O3 相之间的相变途径还不清楚，因为还没有报道过能够产生所有四种 Fe2O3 相的系统合成方法。在此，我们使用介孔 SiO2 报告了一系列 Fe2O3 纳米粒子的合成。Fe2O3 纳米粒子的晶体结构按γ-Fe2O3→ε-Fe2O3→β-Fe2O3→α-Fe2O3 的顺序随粒径增大而变化。使用 FeSO4 作为前驱体进行合成时，估计相变的临界尺寸分别为γ→ε 为 8nm，ε→β 为 30nm，β→α 为 50nm。首次观察到四种 Fe2O3 相之间的相变。
