Nanowire Structural Evolution from Fe₃O₄ to ϵ‐Fe₂O₃

Abstract

Abstract The ϵ‐Fe 2 O 3 phase is commonly considered an intermediate phase during thermal treatment of maghemite (γ‐Fe 2 O 3 ) to hematite (α‐Fe 2 O 3 ). The routine method of synthesis for ϵ‐Fe 2 O 3 crystals uses γ‐Fe 2 O 3 as the source material and requires dispersion of γ‐Fe 2 O 3 into silica, and the obtained ϵ‐Fe 2 O 3 particle size is rather limited, typically under 200 nm. In this paper, by using a pulsed laser deposition method and Fe 3 O 4 powder as a source material, the synthesis of not only one‐dimensional Fe 3 O 4 nanowires but also high‐yield ϵ‐Fe 2 O 3 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 <211> directions, although some stacking faults and twins exist. However, magnetite nanowires growing along the <110> direction are found in every instance to accompany a new phase, ϵ‐Fe 2 O 3 , with some micrometer‐sized wires even fully transferring to ϵ‐Fe 2 O 3 along the fixed structural orientation relationship, (001) ∥ (111) , [010] ∥ <110> . Contrary to generally accepted ideas regarding epsilon phase formation, there is no indication of γ‐Fe 2 O 3 formation during the synthesis process; the phase transition may be described as being from Fe 3 O 4 to ϵ‐Fe 2 O 3 , then to α‐Fe 2 O 3 . 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‐Fe 2 O 3 nanowires. The observed ϵ‐Fe 2 O 3 is fundamentally important for understanding the magnetic properties of the nanowires.