铁和地球发电机输运性质的实验和理论的协调
Reconciliation of experiments and theory on transport properties of iron and the geodynamo
摘要：
来自核心的热量传输量，限制了该地区的动力学和热演化，取决于铁的传输特性。Ohta等人（2016）和Konopkova et al.（2016）在相关的地球核心压力-温度（P-T）条件下，分别在激光加热的金刚石对顶砧单元（DAC）中测量铁的电阻率和热导系数，并获得了非常矛盾的结果。在这里，我们测量hcp-铁的电阻率高达~170 GPa和~3,000 K使用四探针范德堡方法耦合均匀平顶激光加热DAC。我们还计算了它的电导率和热导系数的第一性原理方法，包括电子-声子和电子-电子散射。我们发现，测量的hcp-铁的电阻率随温度的升高几乎呈线性增加，并与当前的第一性原理计算是一致的。hcp-铁的电阻率和热导系数之间的比例系数（洛伦兹数）与理想值（2.44*10^-8 W Ω·K^-2）不同，因此使用~（2.0-2.1）*10^-8 W Ω·K^-2的非理想洛伦兹数将实验电阻率转换为hcp-铁在高P-T下的热导系数。结果表明，在核幔边界附近，hcp铁的电阻率和热导系数分别为80（5）u Ω cm和100（10）W/mK。我们的研究结果表明，通过核-幔边界的液态铁合金外核的绝热热流约为10（1）TW，支持当今地球发电机驱动的热对流通过核心的长期冷却和成分对流通过潜热和重力能在内核的凝固。
英文摘要：
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.
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