Stability of Hydroxylated α-Fe₂O₃(0001) Surfaces

The stability of hydroxylated terminations of the 0001 surface of α-Fe₂O₃ (hematite) is investigated computationally using PBE + U calculations with dispersion corrections. Hydroxylated surfaces with low OH concentrations are found to be most stable in a range of the chemical potential of water of -0.95 eV > μ_H > -2.22 eV. These surfaces can be described as isolated Fe(OH)₃ groups adsorbed on the dry hematite surface and are predicted to be the exposed termination of the 0001 surface in a wide range of relevant experimental conditions. Most investigated reduced surfaces, containing Fe in oxidation state +2, are only stable in a range of the chemical potential of oxygen μ_O < -2.44 eV, where bulk hematite is less than magnetite. The only reduced surface stable at a higher μ_O is derived from the most stable nonreduced hydroxylated surfaces by removing a single OH group per unit cell.