Nanowire Structural Evolution from Fe3O4 to ϵ‐Fe2O3
Abstract
The ϵ‐Fe2O3 phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe2O3) to hematite (α‐Fe2O3). The routine method of synthesis for ϵ‐Fe2O3 crystals uses γ‐Fe2O3 as the source material and requires dispersion of γ‐Fe2O3 into silica, and the obtained ϵ‐Fe2O3 particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe3O4 powder as a source material, the synthesis of not only one‐dimensional Fe3O4 nanowires but also high‐yield ϵ‐Fe2O3 nanowires is reported for the first time. A detailed transmission electron microscopy (TEM) study shows that the nanowires of pure magnetite grow along [111] and directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the direction are found in every instance to accompany a new phase, ϵ‐Fe2O3, with some micrometer‐sized wires even fully transferring to ϵ‐Fe2O3 along the fixed structural orientation relationship, (001) ∥ (111), [010] ∥ . Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe2O3 formation during the synthesis process; the phase transition may be described as being from Fe3O4 to ϵ‐Fe2O3, then to α‐Fe2O3. The detailed structural evolution process has been revealed by using TEM. 120° rotation domain boundaries and antiphase boundaries are also frequently observed in the ϵ‐Fe2O3 nanowires. The observed ϵ‐Fe2O3 is fundamentally important for understanding the magnetic properties of the nanowires.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Mar 15, 2007
- Source ID
- 10.1002/adfm.200601024
Entities
People
- J. R. Morber
- R. L. Snyder
- Yingtao Ding
- Z. L. Wang
Organizations
- National Institutes of Health
- National Science Foundation