First-Principles Study of the Crystal Structure and Elastic Properties of FeO2H2He Under High Pressure

The high 3He/4He ratios in ocean island basalts indicate the presence of an primordial helium reservoir in the Earth's deep interior, while the composition and seismic anomalies of the deep Earth remain key research topics. However, our understanding of stable helium-bearing compounds in the deep Earth is still limited. This study systematically calculated the crystal structure and elastic properties of FeO2H2He at 30–150 GPa using first principles methods based on density functional theory. The static calculation results of phonon dispersion and elastic constants indicate that the R3m cubic crystal structure of FeO2H2He exhibits excellent local dynamic stability and mechanical stability within the studied pressure range. Poisson's ratio and Pugh ratio analyses consistently show that FeO2H2He exhibits a ductile state throughout the investigated pressure range. The comprehensive characteristics of density and wave velocity reveal that FeO2H2He could potentially serve as one of the helium-bearing components near the core-mantle boundary, and may represent a potential mineral component for explaining the wave velocity anomalies observed in ultra-low velocity zones (ULVZs). This research enriches our understanding of the core-mantle boundary composition and provides new mineralogical constraints on the occurrence and distribution of helium in the deep Earth.