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 3O 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 ( aO 2.61– aO 1.00– oh1Fe 2.55– bO 1.00– bO 3.00– td1Fe 1.00– oh2Fe 1.00– td2Fe 1.00–R) to 25% oxygen mixed-iron (OMI) termination ( bO 1.00– bO 3.00– td1Fe 0– oh2Fe 1.00– td2Fe 1.00– aO 3.00– aO 1.00– oh1Fe 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.