Dielectric response of Fe2O3 crystals and thin films

We report the static (ε0) and high frequency (ε∞) dielectric constants of haematite (α-Fe2O3) as calculated using density functional perturbation theory. The values for bulk iron oxide are ε 0 11 = 26.41 ; ε 0 33 = 17.84 ; ε ∞ 11 = 7.87 and ε ∞ 33 = 7.57 . The effective static dielectric screening of porous thin-films is predicted in aqueous solutions, using effective medium theory, to range between 33 and 44 depending on the crystal packing density. The large spread in literature values (12–120) can only be explained through surface and micro-structuring effects. These results will be important for interpreting and modelling the materials behaviour, particularly in electrochemical and photoelectrochemical cells.