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A High-Temperature Electrical Conduction Mechanism in the Lower Mantle Phase (Mg,Fe)1-xO
1Department of Geological Sciences, University College London, London WC1E 6BT, UK.
Science (New York, N.Y.)
|March 21, 1997
Summary
Electrical conductivity in lower mantle magnesiowustite changes with temperature. A shift from small polaron to large polaron conduction at high temperatures impacts models of Earth's deep interior.
Area of Science:
- Geophysics and Mineral Physics
- High-pressure and high-temperature experimental studies
Background:
- Magnesiowustite is a key phase in Earth's lower mantle.
- Previous studies at atmospheric pressure suggested Fe2+-Fe3+ hopping (small polaron) governs conductivity.
Purpose of the Study:
- To investigate the electrical conductivity of magnesiowustite under lower mantle conditions (high pressure and temperature).
- To determine the dominant charge transport mechanism at relevant mantle temperatures.
- To assess the influence of varying Fe3+ content on conductivity.
Main Methods:
- Experimental measurements of electrical conductivity on magnesiowustite.
- Varying pressure, temperature, and Fe3+ content.
- Analysis of charge transport mechanisms based on experimental data.
Main Results:
- Electrical conductivity measurements reveal a temperature-dependent charge transport mechanism.
- At lower temperatures, results align with small polaron conduction.
- At higher temperatures (mantle relevant), a large polaron mechanism is indicated.
Conclusions:
- The charge transport mechanism in magnesiowustite transitions from small to large polaron with increasing temperature.
- This transition has significant implications for interpreting geophysical data and modeling electrical properties of the lower mantle.
- Accurate extrapolation to mantle conditions requires considering this mechanism shift and its compositional dependencies.
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