Research ArticleGEOPHYSICS

Unraveling the complexity of iron oxides at high pressure and temperature: Synthesis of Fe5O6

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Science Advances  26 Jun 2015:
Vol. 1, no. 5, e1400260
DOI: 10.1126/sciadv.1400260
  • Fig. 1 Row of reflections of an Fe5O6 crystal in a multiphase diffraction pattern.

    (A) Detail of an x-ray diffraction pattern collected at 18 GPa, highlighting an indexed row of peaks belonging to an Fe5O6 crystal. (B) In a projection in the reciprocal space of all reflections, those belonging to the Fe5O6 grain are shown in blue.

  • Fig. 2 The structure of Fe5O6.

    The trigonal prisms representing the coordination environment of iron in the 4c position are shown in yellow. Layers of edge-sharing coordination octahedra of iron in the 8f positions are shown in two shades of blue representing two non-equivalent crystallographic sites.

  • Fig. 3 Compositional maps after high P-T synthesis.

    Distribution of the iron oxide phases identified after heating a mixture of hematite and iron at 11 GPa and up to about 2300 K. The maps represent the relative abundances of Fe4O5 (red), Fe5O6 (blue), and wüstite (green). Abundances from 0 to 100% are represented in 10 color shades; deeper colors correspond to higher concentrations. These maps were obtained from 13 × 13 data points and measure 150 μm in both the horizontal and vertical directions.

  • Fig. 4 Bulk compressibility of Fe5O6.

    Data obtained from the grain analysis are represented by solid symbols, and those from the multiphase powder diffraction patterns by crosses. The solid curve represents the fit of a second-order Birch-Murnaghan equation of state (see text). The inset shows the bulk modulus against composition of the three orthorhombic iron oxides h-Fe3O4 (purple), Fe4O5 (red), and Fe5O6 (blue). SD values are smaller than the symbol sizes.

  • Table 1 Structural data of Fe5O6 at 11.4 GPa.

    The least-squares refinement of the unit cell parameters was performed against 200 reflections. The refinement of 10 atomic fractional coordinates and the scale factor was performed against 81 Fo2 (after averaging symmetry equivalents), and converged with satisfactory statistical parameters (R = 10%, Rall = 11%).

    P (GPa)11.4
    T (K)300
    K0 (GPa)173(2)
    a (Å)2.815(10)
    b (Å)9.795(3)
    c (Å)15.011(4)
    V3)414(2)
    <Fe4c-O> (Å)2.076
    <Fe8f1-O> (Å)2.058
    <Fe8f2-O> (Å)2.075
    x, y, z (Fe4c)0, 0.6379(5), ¼
    x, y, z (Fe8f1)0, 0.1341(3), 0.4527(3)
    x, y, z (Fe8f2)0, 0.3959(4), 0.3568(4)
    x, y, z (O1)0, 0.290(2), ¼
    x, y, z (O2)0, 0.782(2), 0.421(2)
    x, y, z (O3)0, 0.043(2), 0.332(2)
    x, y, z (O4)0, ½, 0

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/5/e1400260/DC1

    Fig. S1. Diffraction image (A) and integrated pattern (B) collected during synthesis (~15 GPa, ~2000 K).

    Fig. S2. Diffraction image (A) and integrated pattern (B) collected at 10.7 GPa where Fe5O6, wüstite, neon, and gold were the phases identified.

    Fig. S3. Diffraction image (A) and integrated pattern (B) collected at ~11 GPa where Fe5O6, Fe4O5, and neon were the phases identified.

    Fig. S4. Comparison of the axial compressibility of Fe5O6 and Fe4O5.

    Fig. S5. Volume (A) and relative compressibility (B) of the orthorhombic iron oxides.

    Table S1. Example of cell parameter fitting results from powder diffraction analysis.

    References (3234)

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Diffraction image (A) and integrated pattern (B) collected during synthesis (~15 GPa, ~2000 K).
    • Fig. S2. Diffraction image (A) and integrated pattern (B) collected at 10.7 GPa where Fe5O6, wüstite, neon, and gold were the phases identified.
    • Fig. S3. Diffraction image (A) and integrated pattern (B) collected at ~11 GPa where Fe5O6, Fe4O5, and neon were the phases identified.
    • Fig. S4. Comparison of the axial compressibility of Fe5O6 and Fe4O5.
    • Fig. S5. Volume (A) and relative compressibility (B) of the orthorhombic iron oxides.
    • Table S1. Example of cell parameter fitting results from powder diffraction analysis.
    • References (32–34)

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