Surface structure of magnetite ( 111 ) under hydrated conditions by crystal truncation rod diffraction

Abstract X-ray crystal truncation rod (CTR) diffraction under hydrated conditions at circum-neutral pH was used to determine the surface structure of Fe 3 O 4 (111) following a wet chemical mechanical polishing (CMP) preparation method. The best-fit model to the CTR data shows the presence of two oxygen terminated domains that are chemically inequivalent and symmetrically distinct in the surface contribution ratio of 75% oxygen octahedral-iron (OOI) termination ( a O 2.61 – a O 1.00 – oh1 Fe 2.55 – b O 1.00 – b O 3.00 – td1 Fe 1.00 – oh2 Fe 1.00 – td2 Fe 1.00 –R) to 25% oxygen mixed-iron (OMI) termination ( b O 1.00 – b O 3.00 – td1 Fe 0 – oh2 Fe 1.00 – td2 Fe 1.00 – a O 3.00 – a O 1.00 – oh1 Fe 3.00 –R). An adsorbed water layer could not be constrained in the best-fit model. However, bond-valence analyses suggest that both of the surfaces are hydro-oxo terminated. Furthermore, the topmost iron layers of both domains are inferred to be occupied with the redox active Fe 2+ and Fe 3+ cations indicating that these irons are the principle irons involved in controlling the surface reactivity of magnetite in industrial and environmentally relevant conditions.