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Auxiliary Material for “Highly conductive iron-rich (Mg,Fe)O magnesiowüstite
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and its stability in the Earth's lower mantle”
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K. Ohta,1, 2,* K. Fujino,3 Y. Kuwayama,3 T. Kondo,4 K. Shimizu,1 and Y. Ohishi5
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University, Osaka, Japan
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Tokyo, Japan
Center for Quantum Science and Technology under Extreme Conditions, Osaka
Now at Department of Earth and Planetary Sciences, Tokyo Institute of Technology,
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Geodynamics Research Center, Ehime University, Matsuyama, Ehime, Japan
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Department of Earth and Space Science, Graduate School of Science, Osaka University,
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Toyonaka, Osaka, Japan
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*Corresponding author: K. Ohta, Department of Earth and Planetary Sciences, Tokyo
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Institute of Technology, Meguro, Tokyo 152-8551, Japan. (k-ohta@geo.titech.ac.jp)
Japan Synchrotron Radiation Research Institute, Sayo, Hyogo, Japan
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Introduction
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This Auxiliary Material contains one text file and one figure (Figure A1).
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In the text, we show oxidation of magnesiowüstite sample due to ion-thinning for
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preparation of ATEM observation. Figure A1 shows the X-ray diffraction patterns for
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magnesiowüstite starting materials we report in the manuscript (2014JB010972). The
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XRD patterns clearly show oxidation of magnesiowüstite to magnetite after
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ion-thinning process. Caption of Figure A1 is just below the figure.
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Online supporting information: Oxidation of magnesiowüstite sample during
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ion-thinning process
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We found in this study that the SAED patterns of recovered Mw95-1 and Mw95-2
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samples showed electron diffraction patterns different from the B1 structure (Figure 7).
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On Mw95-2, all the large (>500 nm) grains (1 in Figure 6c for example) with Mg (pcs)
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= 0.04–0.06 revealed the superposition of the strong diffraction pattern of the B1
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structure with a = 4.3 Å and the weak one of the B1-like structure but with the a-axis
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that is double the normal a-axis (Figure 7c), while the small grain (2 in Figure 6c) with
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Mg (pcs) = 0.00 only showed a diffraction pattern similar to the B1-like structure with
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the double a-axis (a = 8.4 Å) (Figure 7d). The SAED patterns from Mw95-1 also
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exhibit the weak patterns of the B1-like phase.
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Here we investigated the effect of ion thinning to phase stability in the sample. We
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performed XRD measurements for (Mg0.20Fe0.80)O and (Mg0.05Fe0.95)O starting
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materials before and after ion thinning. Ion thinning was performed by Gatan Model
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691 PIPS (different from the Ion Slicer used in the present experiments). Ion thinning of
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the pellets of the starting materials was initiated with 5 kV, ~10 A, and the gun angles
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of 8˚ at the initial stage and finished with 3 kV, ~5 A at the final stage in 5-10 hours.
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The XRD patterns of all the starting materials before ion-thinning processing showed
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the B1 structure with a = 4.3 Å, while those of the starting materials after ion-thinning
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processing converted partially to that of magnetite with a = 8.4 Å (Figure A1). The
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results clarified that the change of the SAED patterns from the B1 structure sample with
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a = 4.3 Å to the B1-like structure one with a = 8.4 Å was caused by oxidation of the
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sample due to the ion-thinning process. The possible reason for the oxidation of
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iron-rich magnesiowüstite to magnetite is contamination of the very small amount of
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oxygen in the argon gas, which is irradiated to the samples during ion thinning. The
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degree of oxidation of the samples by the Ion Slicer seems to be smaller than that by the
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PIPS.
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Figure A1. XRD patterns for (Mg0.20Fe0.80)O starting material (a) before and (b) after
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ion-thinning, and for (Mg0.05Fe0.95)O starting material (c) before and (d) after
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ion-thinning. The calculated peak positions of magnesiowüstite (Mw) and magnetite
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(Mgt) are shown by small ticks. X-ray wavelength (λ) is 0.71 Å.
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