Iron-rich Fe-O compounds with closest-packed layers at core pressures

Jin Liu; Yang Sun; Chaojia Lv; Feng Zhang; Suyu Fu; Vitali B. Prakapenka; Cai-Zhuang Wang; Kai-Ming Ho; Jung-Fu Lin; Renata M. Wentzcovitch

paper

Iron-rich Fe-O compounds with closest-packed layers at core pressures

arXiv:2110.00524

Abstract

Oxygen solubility in solid iron is extremely low, even at high pressures and temperatures. Thus far, no Fe-O compounds between Fe and FeO endmembers have been reported experimentally. We observed chemical reactions of Fe with FeO or Fe $_{2}$ O $_{3}$ $in s i t u$ x-ray diffraction experiments at 220-260 GPa and 3,000-3,500 K. The refined diffraction patterns are consistent with a series of Fe $_{n}$ O (n $>$ 1) compounds (e.g., Fe $_{25}$ O $_{13}$ and Fe $_{28}$ O $_{14}$ ) identified using the adaptive genetic algorithm. Like $ε$ -Fe in the hexagonal close-packed (hcp) structure, the structures of Fe $_{n}$ O compounds consist of oxygen-only close-packed monolayers distributed between iron-only layers. $A b ini t i o$ calculations show systematic electronic properties of these compounds that have ramifications for the physical properties of Earth's inner core.

6 pages, 4 figures