High‐Temperature Equation of State of FeH: Implications for Hydrogen in Earth's Inner Core
Shoh Tagawa, Hitoshi Gomi, Kei Hirose, Yasuo Ohishi
Abstract
Abstract While hydrogen is one of plausible major light elements in the core, the high‐temperature equation of state (EoS) of Fe‐H alloy has not been experimentally examined to the core pressure range. Here we measured the volume ( V ) of non‐magnetic (NM) face‐centered cubic (fcc) FeH at high pressure and temperature ( P‐T ) to 142 GPa and 3660 K in a laser‐heated diamond‐anvil cell and obtained its P‐V‐T EoS. An increase in the lattice volume of Fe per H atom, Δ V H , determined as functions of P and T is found to be substantially smaller than the volume of metallic H that has been used to estimate H concentration in Fe‐H alloy. The Δ V H is almost identical between fcc and double hexagonal close‐packed phases in the NM state, suggesting that it may be applicable to hcp. The extrapolation of Δ V H to inner core conditions indicates its maximum H content to be 0.8–0.9 wt%.