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.com
Volume 3, Issue 2
ISSN: 2470-9905
Crystallography 2017
October 16-17, 2017
2
nd
International Conference on
October 16-17, 2017 | Chicago, USA
Applied Crystallography
Asize dependent phase map and phase transformation kinetics for iron(III) oxide nanomaterials (γ →ε→α
pathway)
Seungyeol Lee
and
Huifang Xu
University of Wisconsin-Madison, USA
N
anometric iron(III)-oxide has been of great interest in a wide range of fields due to magnetic properties, eminent biochemical
characteristics and potential for technological applications. To date, five crystalline polymorphs of Fe
2
O
3
are known: (1) α-Fe
2
O
3
(i.e., hematite), (2) β-Fe
2
O
3
, (3) γ-Fe
2
O
3
(i.e., maghemite), (4) ε-Fe
2
O
3
(i.e., luogufengite),and (5) ζ-Fe
2
O
3
, all of which have different
morphologies, various size and magnetic properties. Among the iron-oxides, ε-Fe
2
O
3
is considered as a remarkable phase due to its
giant coercive field at room temperature and ferromagnetic resonance capability. The natural ε-Fe
2
O
3
(luogufengite) is discovered
from vesicles’ surfaces of basaltic scoria. Here we present the first size-dependent phase map for ε-Fe
2
O
3
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-Fe
2
O
3
nanocrystals show the inversion and pseudo-hexagonal
twins, which are fundamentally important for understanding the correlation between its nanostructure and magnetic properties.
Two activation energies for γ-Fe
2
O
3
→α-Fe
2
O
3
phase transformations are 186.37±9.89 kJ mol
-1
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 such as designing engineered materials. Combining the phase map with their kinetic properties predicts that
stability regime of the nanosized Fe
2
O
3
polymorphs as the function of crystal size, temperature and annealing times. The proposed
size-dependent phase map will help to improve controlled synthesis of ε-Fe
2
O
3
nanocrystal, a promising material for many future
applications.
Lee572@wisc.eduStruct Chem Crystallogr Commun, 3:2
DOI: 10.21767/2470-9905-C1-003