title: First observation of phase transformation of all four Fe(2)O(3) phases (gamma --> epsilon --> beta --> alpha-phase).
abstract: 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.
authors: Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors: Shunsuke
authors: S
authors: Sakurai
authors: Asuka
authors: A
authors: Namai
authors: Kazuhito
authors: K
authors: Hashimoto
authors: Shin-Ichi
authors: S
authors: Ohkoshi