The Fe3O4 origin of the “Biphase” reconstruction on α-Fe2O3(0 0 0 1)

The so-called Biphase termination on α-Fe2O3 has been widely accepted to be a structure with a ∼40 Å unit supercell composed of coexisting islands of Fe1−xO and α-Fe2O3. Based on thermodynamic arguments and experimental evidence, including transmission electron diffraction, imaging, magnetic and spectroscopic information, it is found that the previously proposed structure model is inaccurate. The actual Biphase structure is instead a layered structure related to the reduction of α-Fe2O3 to Fe3O4. A model for the Biphase termination is proposed which does not contain islands of Fe1−xO but instead consists of bulk α-Fe2O3 and a Fe3O4-derived overlayer. The proposed model is consistent with all current and previously reported experimental findings.