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Discovery of the recoverable high-pressure iron oxide Fe4O5

  1. Yusheng Zhaoa,b
  1. aHigh Pressure Science and Engineering Center, University of Nevada, Las Vegas, NV 89154;
  2. bDepartment of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154;
  3. cGeoSoilEnviroCARS, Center for Advanced Radiation Sources, University of Chicago, Argonne, IL 60439;
  4. dHigh Pressure Collaborative Access Team, Carnegie Institution of Washington, Argonne, IL 60439;
  5. eGeosciences, University of Arizona, Tucson, AZ 85721-0077; and
  6. 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)

  1. Fig. 1.

    The single crystal of Fe4O5 synthesized in the diamond anvil cell at high pressure after laser heating. The sample chamber, about 60?μm in diameter, viewed through a diamond anvil at 10?GPa and its sketch show the rounded opaque crystal of Fe4O5 grown in the heated area. The sample is well separated from the gasket, ruby, and the anvils by the inert neon medium.

  2. Fig. 2.

    Structure of Fe4O5. Green and blue octahedra (sites Fe1 and Fe2, respectively) illustrate nonequivalent edge-sharing FeO6 groups forming layers perpendicular to the c axis. Layers are alternated by channels where iron, represented as red spheres (Site Fe3), is arranged in larger triangular prisms sharing faces along the direction of the a axis.

  3. Fig. 3.

    Compressibility of Fe4O5. Pressure dependence of lattice parameters and volume of the unit cell. Data are from single crystal (open diamonds), two separate powder diffraction experiments (red and green circles), and from first-principles calculations (blue squares). Dashed black trends, interpolated from powder diffraction data, are reported as a visual aid. Standard deviations are smaller than the symbol sizes.

  4. 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, ΔHc?=?H(Fe4O5)?-?[H(FeO)?+?H(c-Fe3O4)] and ΔHh?=?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, ΔHh (the reference), and ΔHc, respectively. ΔHc is extracted from the literature (15). The Fe4O5 structure is favored over the sum of breakdown products at 10?GPa.

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