Discovery of the recoverable high-pressure iron oxide Fe₄O₅

Abstract

Phases of the iron–oxygen binary system are significant to most scientific disciplines, directly affecting planetary evolution, life, and technology. Iron oxides have unique electronic properties and strongly interact with the environment, particularly through redox reactions. The iron–oxygen phase diagram therefore has been among the most thoroughly investigated, yet it still holds striking findings. Here, we report the discovery of an iron oxide with formula Fe 4 O 5 , synthesized at high pressure and temperature. The previously undescribed phase, stable from 5 to at least 30 GPa, is recoverable to ambient conditions. First-principles calculations confirm that the iron oxide here described is energetically more stable than FeO + Fe 3 O 4 at pressure greater than 10 GPa. The calculated lattice constants, equation of states, and atomic coordinates are in excellent agreement with experimental data, confirming the synthesis of Fe 4 O 5 . Given the conditions of stability and its composition, Fe 4 O 5 is a plausible accessory mineral of the Earth’s upper mantle. The phase has strong ferrimagnetic character comparable to magnetite. The ability to synthesize the material at accessible conditions and recover it at ambient conditions, along with its physical properties, suggests a potential interest in Fe 4 O 5 for technological applications.

High-Fe (Mg, Fe)O inclusion in diamond apparently from the lowermost mantle

“…Because the composition of the actual phase present is approximately (Mg 0.5 Fe 0.5 )Fe 2 O 4 , it is not clear whether the phase of this composition would crystallize at extreme pressures in the CaMn 2 O 4 structure (like pure magnesium ferrite, MgFe 2 O 4 ) (Andrault and Bolfan-Casanova, 2001;Levy et al, 2004;Winell et al, 2006), or whether the situation might be more complicated. Recent work has shown that pure magnetite decomposes into a mixture of Fe 2 O 3 (hematite) and the newly-discovered Fe 4 O 5 structure (Lavina et al, 2011;Woodland et al, 2012). Fig.…”

Metal-insulator transition and the role of electron correlation in FeO2

“…Among them, FeO and Fe 2 O 3 are two end members and the most well-known compounds. However other kinds of iron oxides with new stoichiometry, such as Fe 4 O 5 [2] and Fe 5 O 6 [3], are also discovered under the high pressure and temperature. Recently FeO 2 , which holds an excessive amount of oxygen, is identified with both first-principles calculation and experiment near 76 GPa [1].…”

Synthesis of a quenchable high-pressure form of magnetite (h-Fe3O4) with composition Fe1(Fe2+0.75Mg0.26)Fe2(Fe3+0.70Cr0.15Al0.11Si0.04)2O4

“…The high-pressure Fe-oxide, Fe 4 O 5 is stable from 5 to at least 30 GPa, and is recoverable to ambient conditions (Lavina et al 2011). They synthesized Fe 4 O 5 in a pure Fe-O system, using mixtures of Fe and Fe 3 O 4 as starting material, at P = 10 and 20 GPa, and T between 1227 and 1927 °C and refined the structure as isostructural with CaFe 3 O 5 (space group Cmcm).…”

“…The discovery of the high-pressure Fe-oxide Fe 4 O 5 (Lavina et al 2011) (Hazen and Jeanloz 1984). It crystallizes in the cubic NaCl-type structure and forms a solid solution series with MgO (periclase).…”

“…Thus, the structure is very similar to h-Fe 3 O 4 . Lavina et al (2011) (2) a Fe-dominated oxide mixture plus Cr-, Mg-and Si-oxides. Surprisingly, the structure was quenchable in both types of experiments to ambient conditions, which allowed us to collect precise electron diffraction data by automated electron diffraction tomography (ADT).…”