| Abstract
| - The nanowire form of ε-Fe2O3 single crystal was prepared by combining the reverse-micelle and sol−gel methods. To elucidate the detailed formation process of ε-Fe2O3 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(NO3)3 and Ba(NO3)2 was 7.5 ± 2.1 nm, whereas that in another reverse-micelle containing NH3 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(C2H5O)4, Fe(OH)3 was covered by SiO2 through the hydrolysis reaction. TEM observations showed that the size of Fe(OH)3 nanoparticles in the SiO2 matrix was 5 ± 1 nm. By heating to 900 °C, Fe(OH)3 transformed into spherical-shaped γ-Fe2O3 (Fd3̅m, a = 8.35 Å) without changing size. Moreover, upon heating the sample to 1025 °C, nanorod-type ε-Fe2O3 (Pna21, 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-Fe2O3 nanorod, and the long axis length of ε-Fe2O3 nanowire reached 1.5 μm. This is the first example of a nanowire form of ε-Fe2O3 single crystal.
|
