Exploring (1$$overline{1}$$2)-related ordered structure in oxidation-synthesized α-Fe₂O₃ nanowhiskers

Hematite (α-Fe₂O₃) nanowhiskers (NWs) synthesized via oxidation of iron-based substrates are a promising photoanode material for photoelectrochemical water splitting. Such synthesized α-Fe₂O₃ NWs have been found to contain ordered axial structures. Herein, we reveal that the known (1$$overline{1}$$2)-related ordered structure actually exists in bicrystalline α-Fe₂O₃ NWs instead of single-crystalline α-Fe₂O₃ NWs and that it is associated with another known (3$$overline{3}$$0)-related ordered structure. Through a spherical aberration (CS)-corrected high-resolution transmission electron microscopy (HR-TEM) investigation, the microstructural characteristic of the (1$$overline{1}$$2)-related ordered structure is verified to be periodic atomic column displacements serving as tensile strain accommodation. The HR-TEM observation are also supported by a monochromated O K-edge EELS analysis, which indicates that α-Fe₂O₃ NWs hosting the (1$$overline{1}$$2)-related ordered structure are indeed associated with lattice expansion. In sum, our microstructural study elucidates the root cause of the long-asserted relationship between the (1$$overline{1}$$2)-related ordered structure and oxygen vacancy ordering