Electrical resistivity, thermal conductivity, and viscosity of Fe-H alloys at Earth's core conditions

Cong Liu, Ronald Cohen
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Abstract

The transport properties (electrical resistivity, thermal conductivity, and viscosity) of iron-hydrogen alloy are of great significance in the stability and evolution of planetary magnetic fields. Here, we investigate the thermal transport properties of iron doped with varying hydrogen content as functions of pressure (P) and temperature (T) for the top and bottom of Earth's outer core and beyond, corresponding to pressures of about 130 to 300 GPa and temperatures of 4000 to 7000 K. Using first-principles density functional theory molecular dynamic simulations (FPMD), we verify that crystalline FeH$_x$ is superionic with H diffusing freely. We find a low frequency viscosity of 10-11 mPa$\cdot$s for liquid Fe-H alloys at Earth's outer core conditions by the linear response Green-Kubo formula. Using the KKR method within density functional theory (DFT) plus Dynamical mean-field Theory (DMFT), we find saturation of electrical resistivity with increasing temperatures in liquid iron at outer core conditions. The effect of H on electrical and thermal transport we find is small, so that the exact H content of the core is not needed. The primary effect of H is on the equation of state, decreasing the density at constant P and T. We find the Lorenz number is smaller than the ideal value, and obtain for X(H)= 0.20, or 0.45 wt% H , thermal conductivity $\kappa$ of $\sim$105 and $\sim$190 $Wm^{-1}K^{-1}$, respectively, at conditions near the core-mantle and inner-outer core boundary.
地核条件下 Fe-H 合金的电阻率、热导率和粘度
铁氢合金的传输特性(电阻率、热导率和粘度)对行星磁场的稳定和演化具有重要意义。利用第一原理密度泛函理论分子动力学模拟(FPMD),我们验证了结晶的 FeH$_x$ 是超离子的,H 可以自由扩散。通过线性响应格林-久保公式,我们发现液态 Fe-H 合金在地球外核条件下的低频粘度为 10-11 mPa$\cdot$s。利用密度函数理论(DFT)和动态平均场理论(DMFT)中的 KKR 方法,我们发现外核条件下液态铁的电阻率会随着温度的升高而饱和。我们发现 H 对电学和热学传输的影响很小,因此不需要确切的铁芯 H 含量。我们发现洛伦兹数小于理想值,并得到了 X(H)= 0.20 或 0.45 wt% H 的热导率$\kappa$分别为$\sim$105 和$\sim$190 $Wm^{-1}K^{-1}$,其条件靠近内核-外核边界。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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