Powder XRD analyses of the surface of the HF and OS samples.
a) Le Bail fit of the HF Fe-rich surface region, showing the presence of hematite and ε-Fe2O3; b) Le Bail fit of the OS Fe-rich surface region, showing the presence of ε-Fe2O3. For a) and b), powder patterns were recorded with a Bruker D8 Advanced and a beam of ~100 μm in diameter. The high intensity of the 002 reflection at 18.84° (2θ CuKα) indicates preferred orientation. c) 2D diffraction pattern obtained from the surface of the HF sample, from a low content Fe zone (HF-Surf-G) and from a Fe-rich region (HF-Surf-Fe). Theoretical positions for the ε-Fe2O3 are indicated in red; d) 2D diffraction pattern obtained from 2 Fe-rich regions at the surface of the OS sample. Theoretical positions for the ε-Fe2O3 are indicated in red. For c) and d), 2D patterns were obtained at ALS beamline 12.3.2 using a ~15 μm*15 μm microbeam. While the 2D diffraction rings look homogeneous for HF-Surf-Fe, they are highly textured for OS-Surf-Fe.