| 초록 |
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, epsilon;-Fe 2 O 3 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 epsilon;-Fe 2 O 3 via a gamma; rarr; epsilon; rarr; alpha; 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 epsilon;-Fe 2 O 3 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 gamma;-Fe 2 O 3 rarr; alpha;-Fe 2 O 3 phase transformations are 186.37 ± 9.89 and 174.58 ± 2.24 kJ mol ndash;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. Graphic Abstract ACS Electronic Supporting Info |
