Liquid iron‐hydrogen alloys at outer core conditions by first‐principles calculations

Abstract

AbstractWe examined the density, bulk sound (compressional) velocity, and Grüneisen parameter of liquid pure Fe, Fe100H28 (0.50 wt % H), Fe88H40 (0.81 wt % H), and Fe76H52 (1.22 wt % H) at Earth's outer core pressure and temperature (P‐T) conditions (~100 to 350 GPa, 4000 to 7000 K) based on first‐principles molecular dynamics calculations. The results demonstrate that the thermodynamic Grüneisen parameter of liquid iron alloy decreases with increasing pressure, temperature, and hydrogen concentration, indicating a relatively small temperature gradient in the outer core when hydrogen is present. Along such temperature profile, both the density and compressional velocity of liquid iron containing ~1 wt % hydrogen match seismological observations. It suggests that hydrogen could be a primary light element in the core, although the shear velocity of the inner core is not reconciled with solid Fe‐H alloy and thus requires another impurity element.