Stability of fcc phase FeH to 137 GPa

• Published in: The American mineralogist Vol. 105; no. 6; pp. 917 - 921
• Main Authors: Kato, Chie, Umemoto, Koichiro, Ohta, Kenji, Tagawa, Shoh, Hirose, Kei, Ohishi, Yasuo
• Format: Journal Article
• Language: English
• Published: Washington Mineralogical Society of America 01.06.2020; Walter de Gruyter GmbH
• Subjects: ab initio calculation; Approximation; Compressibility; core; Crystal structure; Earth’s core; experimental studies; Experiments; face-centered cubic structure; fcc structure; FeH; Geophysics; High pressure; Hydrogen; interior; iron; iron hydride; Magnetic transitions; metals; Mineralogy; P-T conditions; Phase diagrams; Phase transitions; pressure; related to mantle; solid Earth (tectonophysics); Stability; Temperature; ultrahigh pressure; Unit cell; X-ray diffraction data; X-rays; X‑ray diffraction
• ISSN: 0003-004X; 1945-3027
• DOI: 10.2138/am-2020-7153

We examined the crystal structure of FeHX (X∼1) (FeH hereafter) at high pressure and temperature by X-ray diffraction up to 137 GPa. Results show that FeH adopts a face-centered cubic (fcc) structure at pressures of 43 to 137 GPa and temperatures of ∼1000 to 2000 K. Our study revises a phase diagram of stoichiometric FeH in which fcc has a wider-than-expected stability field at high pressure and temperature. Based on our findings, the FeH end-member of the Fe-FeH system is expected to be stable in the fcc structure at the P-T conditions of the Earth's core, rather than in the double-hexagonal close packed (dhcp) structure as previously reported. We compared the experimentally determined unit-cell volumes of FeH with those from ab initio calculations. Additionally, we observed a change in compressibility at ∼60 GPa, which could be attributed to a magnetic transition - an interpretation supported by our ab initio computations.