Fig. 4.

Enthalpies of Fe₄O₅ and of the plausible breakdown oxides FeO and h-Fe₃O₄. To examine the relative stability of Fe₄O₅ with respect to its possible breakdown products (FeO and Fe₃O₄ in the ambient and high-pressure structures), the enthalpy differences, ΔH^c = H(Fe₄O₅) - [H(FeO) + H(c-Fe₃O₄)] and ΔH^h = H(Fe₄O₅) - [H(FeO) + H(h-Fe₃O₄)], were calculated as a function of pressure. The solid, dashed, and dot-dashed lines represent the enthalpies of Fe₄O₅, ΔH^h (the reference), and ΔH^c, respectively. ΔH^c is extracted from the literature (15). The Fe₄O₅ structure is favored over the sum of breakdown products at 10 GPa.