Preparation of the Nanowire Form of ε-Fe2O3Single Crystal and a Study of the Formation Process

The nanowire form of ε-Fe 2 O 3 single crystal was prepared by combining the reverse-micelle and sol−gel methods. To elucidate the detailed formation process of ε-Fe 2 O 3 nanowires, the morphology of a sample at each process was measured using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). SAXS measurements showed that the diameter of the water phase in a reverse-micelle containing Fe(NO 3 ) 3 and Ba(NO 3 ) 2 was 7.5 ± 2.1 nm, whereas that in another reverse-micelle containing NH 3 was 6.5 ± 2.0 nm. Mixing these two solutions caused the hydroxylation reaction in the water phase, which yielded Fe(OH) 3 nanoparticles. By injecting Si(C 2 H 5 O) 4, Fe(OH) 3 was covered by SiO 2 through the hydrolysis reaction. TEM observations showed that the size of Fe(OH) 3 nanoparticles in the SiO 2 matrix was 5 ± 1 nm. By heating to 900 °C, Fe(OH) 3 transformed into spherical-shaped γ-Fe 2 O 3 ( Fd 3̅ m, a = 8.35 Å) without changing size. Moreover, upon heating the sample to 1025 °C, nanorod-type ε-Fe 2 O 3 ( Pna 2 1, a = 5.10 Å, b = 8.78 Å, c = 9.47 Å) was obtained. Barium adsorption to the crystal induced anisotropic growth along the crystallographic a -axis of the ε-Fe 2 O 3 nanorod, and the long axis length of ε-Fe 2 O 3 nanowire reached 1.5 μm. This is the first example of a nanowire form of ε-Fe 2 O 3 single crystal.