Mechanism of the lattice relaxation in thin epitaxial films of iron oxides: Generalization from the case of ilmenite–hematite solid solution

The overshoot of the in-plane lattice parameter above its expected value was previously observed for iron oxides on different substrates for initial stages of the film growth. The reasons for the overshoot provided in the previously published experimental studies have not satisfactorily explained the effect. In the present article the overshoot is explained in terms of the surface atom displacements at low thicknesses due to the strong lattice relaxation via dislocation formation. The ilmenite–hematite solid solution is used as an example for the experimental and theoretical descriptions of the overshoot. The theoretical model, based on the dislocation density, can be directly applied to describe the lattice relaxation as a function of the film thickness for other iron-based oxide films with a strong film/substrate lattice mismatch.