We report the formations of fcc and distorted hcp iron-helium compounds with x in FeHex up to 0.13 and 0.48, respectively, based on experiments at 5-54 GPa and ~1000-2820 K. Upon releasing pressure under room temperature, these fcc and distorted hcp FeHex were still observed by XRD and SIMS measurements. Our first-principles calculations indicate that fcc and hcp FeHex, with helium atoms occupying the tetrahedral and trigonal-planar interstitial sites (instead of the octahedral sites), are dynamically stable throughout 0-50 GPa. These results support that the Earth's core can be a large reservoir of primordial 3He.
@article{arxiv.2405.11810,
title = {Formation of Iron-Helium Compounds under High Pressure},
author = {Haruki Takezawa and Han Hsu and Kei Hirose and Fumiya Sakai and Suyu Fu and Hitoshi Gomi and Shiro Miwa and Naoya Sakamoto},
journal= {arXiv preprint arXiv:2405.11810},
year = {2024}
}