Iron oxide equation

1. bDepartment of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154;
2. cGeoSoilEnviroCARS, Center for Advanced Radiation Sources, University of Chicago, Argonne, IL 60439;
3. dHigh Pressure Collaborative Access Team, Carnegie Institution of Washington, Argonne, IL 60439;
4. eGeosciences, University of Arizona, Tucson, AZ ; and
5. fDepartment of Chemistry, University of Nevada, Las Vegas, NV 89154

1. Edited by Alexandra Navrotsky, University of California, Davis, CA, and approved August 29, 2011 (received for review May 13, 2011)

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 Fe4O5, 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 + Fe3O4 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 Fe4O5. Given the conditions of stability and its composition, Fe4O5 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 Fe4O5 for technological applications.

Footnotes

• Author contributions: B.L. designed research; B.L. and E.K. performed research; B.L. and P.D. analyzed data; and B.L., P.D., E.K., Y.M., R.T.D., P.F.W., S.R.S., and Y.Z. wrote the paper.
• The authors declare no conflict of interest.
• This article is a PNAS Direct Submission.