Atomic Structure of the Fe<sub>3</sub>O<sub>4</sub>/Fe<sub>2</sub>O<sub>3</sub> Interface During Phase Transition from Hematite to Magnetite
Xiaoben Zhang, Chuanchuan Jin, Shaobo Han, Peiyao Guo, Yan Zhou, Wei Liu, Wenjie Shen
Abstract
Phase transition between iron oxides practically defines their functionalities in both physical and chemical applications. Direct observation of the atomic rearrangement and a quantitative description of the dynamic behavior of the phase transition, however, are rare. Here, we monitored the structure evolution from a rod-shaped hematite nanoparticle to magnetite during H 2 reduction at elevated temperatures. Environmental transmission electron microscopy observations, along with selected area electron diffraction experiments, identified that the reduction preferentially commenced with Fe 3 O 4 nucleation on the surface defective sites, followed by laterally growing into a Fe 3 O 4 film until fully covering the particle surface. The Fe 3 O 4 phase then propagated toward the bulk particle via a Fe 3 O 4 /α-Fe 2 O 3 interface with the relationship α-Fe 2 O 3 (0001)//Fe 3 O 4 (111) in an aligned orientation of [112] Fe 3 O 4 ||[112̅0] α-Fe 2 O 3 . Upon this Fe 3 O 4 /α-Fe 2 O 3 interface, the Fe–O octahedra in Fe 3 O 4 (111) (as layer A) matches that of α-Fe 2 O 3 (0001) at a rotation angle of 30°, and the reduction proceeds in such a pattern that two-thirds of the Fe Oh in the adjacent layer (layer B) is transformed into Fe Te .