Reconciliation of experiments and theory on transport properties of iron and the geodynamo

Abstract

The amount of heat transport from the core, which constrains the dynamics and thermal evolution of the region, depends on the transport properties of iron. Ohta et al.(2016) and Konopkova et al.(2016) measured electrical resistivity and thermal conductivity of iron, respectively, in laser-heated diamond anvil cells (DACs) at relevant Earth's core pressure-temperature (P-T) conditions, and obtained dramatically contradictory results. Here we measure the electrical resistivity of hcp-iron up to ~170 GPa and ~3,000 K using a four-probe van der Pauw method coupled with homogeneous flat-top laser-heating in a DAC. We also compute its electrical and thermal conductivity by first-principles methods including electron-phonon and electron-electron scattering. We find that the measured resistivity of hcp-iron increases almost linearly with increasing temperature, and is consistent with current first-principles computations. The proportionality coefficient between resistivity and thermal conductivity (the Lorenz number) in hcp-iron differs from the ideal value (2.44*10^-8 W Omega K^-2), so a non-ideal Lorenz number of ~(2.0-2.1)*10^-8 W Omega K^-2 is used to convert the experimental resistivity to the thermal conductivity of hcp-Fe at high P-T. The results constrain the resistivity and thermal conductivity of hcp-iron to ~80(5) u Omega cm and ~100(10) W/mK, respectively, at conditions near core-mantle boundary. Our results indicate an adiabatic heat flow of ~10(1) TW through the core-mantle boundary for a liquid Fe alloy outer core, supporting a present-day geodynamo driven by thermal convection through the core's secular cooling and by compositional convection through the latent heat and gravitational energy during the inner core's solidification.

39 pages, 14 figures

References in corpus (2)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Thermal conductivity of MgO, MgSiO3 perovskite and post-perovskite in the Earth's deep mantle

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• Thermal Evolution and magnetic history of rocky planets
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• Impact of Electronic Correlations on High-Pressure Iron: Insights from Time-Dependent Density Functional Theory
• Thermal conductivity of iron and nickel during melting: Implication to Planetary liquid outer core
• Revisiting the Fermion Sign Problem from the Structure of Lee-Yang Zeros. I. The Form of Partition Function for Indistinguishable Particles and Its Zeros at 0~K
• Structure and Melting of Fe, MgO, SiO2, and MgSiO3 in Planets: Database, Inversion, and Phase Diagram