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The effect of iron spin transition on electrical conductivity of (Mg,Fe)O magnesiowüstite.

Ohta K, Hirose K, Onoda S, Shimizu K - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2007)

Bottom Line: The results demonstrate that the electrical conductivity increases with increasing pressure to about 60 GPa and exhibits anomalous behavior at higher pressures; it conversely decreases to around 80 GPa and again increases very mildly with pressure.A very small pressure effect on the electrical conductivity above 80 GPa suggests that a dominant conduction mechanism changes by this electronic spin transition.The electrical conductivity below 2000-km depth in the mantle may be much smaller than previously thought, since the spin transition takes place also in (Mg,Fe)SiO3 perovskite.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan .

ABSTRACT
We measured the electrical conductivity of Mg0.81Fe0.19O magnesiowüstite, one of the important minerals comprising Earth's lower mantle, at high pressures up to 135 GPa and 300 K in a diamond-anvil cell (DAC). The results demonstrate that the electrical conductivity increases with increasing pressure to about 60 GPa and exhibits anomalous behavior at higher pressures; it conversely decreases to around 80 GPa and again increases very mildly with pressure. These observed changes may be explained by the high-spin to low-spin transition of iron in magnesiowüstite that was previously reported to occur in a similar pressure range. A very small pressure effect on the electrical conductivity above 80 GPa suggests that a dominant conduction mechanism changes by this electronic spin transition. The electrical conductivity below 2000-km depth in the mantle may be much smaller than previously thought, since the spin transition takes place also in (Mg,Fe)SiO3 perovskite.

No MeSH data available.


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(a) Cross section of experimental set up. (b) Photograph and schematic drawing showing the configuration of the sample and electrodes on the diamond-anvil. The gold foils were attached to the sample and connected to platinum electrodes outside the sample hole.
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f1-83_097: (a) Cross section of experimental set up. (b) Photograph and schematic drawing showing the configuration of the sample and electrodes on the diamond-anvil. The gold foils were attached to the sample and connected to platinum electrodes outside the sample hole.

Mentions: We measured the electrical conductivity of polycrystalline magnesiowüstite containing 19 mol% iron with Fe3+/(Fe2++Fe3+) ratio of 0.013. The ferric iron content in our sample was estimated according to the method by Dobson et al.14) High-pressure conditions were generated in a DAC (Fig. 1). The beveled diamond anvils with 150- or 200-μm culet were used. We indented the rhenium gasket to about 50-μm thick, and then made a hole at its center, and put Al2O3 powder in it and on the rhenium. They were subsequently compressed for Al2O3 to be transparent. The magnesiowüstite sample was loaded into a hole with 60-μm diameter that was drilled in Al2O3. Two electrodes made of platinum foil were placed on the Al2O3 layer, which electrically insulated the sample and electrodes against rhenium. From these Pt electrodes, we put another platinum or gold electrodes directly attached to the sample. No pressure medium was loaded so as to ensure a good contact between sample and electrodes.


The effect of iron spin transition on electrical conductivity of (Mg,Fe)O magnesiowüstite.

Ohta K, Hirose K, Onoda S, Shimizu K - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2007)

(a) Cross section of experimental set up. (b) Photograph and schematic drawing showing the configuration of the sample and electrodes on the diamond-anvil. The gold foils were attached to the sample and connected to platinum electrodes outside the sample hole.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3756880&req=5

f1-83_097: (a) Cross section of experimental set up. (b) Photograph and schematic drawing showing the configuration of the sample and electrodes on the diamond-anvil. The gold foils were attached to the sample and connected to platinum electrodes outside the sample hole.
Mentions: We measured the electrical conductivity of polycrystalline magnesiowüstite containing 19 mol% iron with Fe3+/(Fe2++Fe3+) ratio of 0.013. The ferric iron content in our sample was estimated according to the method by Dobson et al.14) High-pressure conditions were generated in a DAC (Fig. 1). The beveled diamond anvils with 150- or 200-μm culet were used. We indented the rhenium gasket to about 50-μm thick, and then made a hole at its center, and put Al2O3 powder in it and on the rhenium. They were subsequently compressed for Al2O3 to be transparent. The magnesiowüstite sample was loaded into a hole with 60-μm diameter that was drilled in Al2O3. Two electrodes made of platinum foil were placed on the Al2O3 layer, which electrically insulated the sample and electrodes against rhenium. From these Pt electrodes, we put another platinum or gold electrodes directly attached to the sample. No pressure medium was loaded so as to ensure a good contact between sample and electrodes.

Bottom Line: The results demonstrate that the electrical conductivity increases with increasing pressure to about 60 GPa and exhibits anomalous behavior at higher pressures; it conversely decreases to around 80 GPa and again increases very mildly with pressure.A very small pressure effect on the electrical conductivity above 80 GPa suggests that a dominant conduction mechanism changes by this electronic spin transition.The electrical conductivity below 2000-km depth in the mantle may be much smaller than previously thought, since the spin transition takes place also in (Mg,Fe)SiO3 perovskite.

View Article: PubMed Central - PubMed

Affiliation: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo, Japan .

ABSTRACT
We measured the electrical conductivity of Mg0.81Fe0.19O magnesiowüstite, one of the important minerals comprising Earth's lower mantle, at high pressures up to 135 GPa and 300 K in a diamond-anvil cell (DAC). The results demonstrate that the electrical conductivity increases with increasing pressure to about 60 GPa and exhibits anomalous behavior at higher pressures; it conversely decreases to around 80 GPa and again increases very mildly with pressure. These observed changes may be explained by the high-spin to low-spin transition of iron in magnesiowüstite that was previously reported to occur in a similar pressure range. A very small pressure effect on the electrical conductivity above 80 GPa suggests that a dominant conduction mechanism changes by this electronic spin transition. The electrical conductivity below 2000-km depth in the mantle may be much smaller than previously thought, since the spin transition takes place also in (Mg,Fe)SiO3 perovskite.

No MeSH data available.


Related in: MedlinePlus