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The amount of heat transport from the core, which constrains the dynamics andthermal evolution of the region, depends on the transport properties of iron.Ohta et al.(2016) and Konopkova et al.(2016) measured electrical resistivityand thermal conductivity of iron, respectively, in laser-heated diamond anvilcells (DACs) at relevant Earth's core pressure-temperature (P-T) conditions,and obtained dramatically contradictory results. Here we measure the electricalresistivity of hcp-iron up to ~170 GPa and ~3,000 K using a four-probe van derPauw method coupled with homogeneous flat-top laser-heating in a DAC. We alsocompute its electrical and thermal conductivity by first-principles methodsincluding electron-phonon and electron-electron scattering. We find that themeasured resistivity of hcp-iron increases almost linearly with increasingtemperature, and is consistent with current first-principles computations. Theproportionality coefficient between resistivity and thermal conductivity (theLorenz number) in hcp-iron differs from the ideal value (2.44*10^-8 W OmegaK^-2), so a non-ideal Lorenz number of ~(2.0-2.1)*10^-8 W Omega K^-2 is used toconvert the experimental resistivity to the thermal conductivity of hcp-Fe athigh P-T. The results constrain the resistivity and thermal conductivity ofhcp-iron to ~80(5) u Omega cm and ~100(10) W/mK, respectively, at conditionsnear 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 thecore's secular cooling and by compositional convection through the latent heatand gravitational energy during the inner core's solidification.

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