Structural transition and re-emergence of iron's total electron spin in (Mg,Fe)O at ultrahigh pressure.
basic_science · Level V
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- Record sourced from PubMed, PMID 35589702.
- Also identified by DOI 10.1038/s41467-022-30100-5 and PMC identifier 9120148.
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Abstract
Fe-bearing MgO [(Mg<sub>1-x</sub>Fe<sub>x</sub>)O] is considered a major constituent of terrestrial exoplanets. Crystallizing in the B1 structure in the Earth's lower mantle, (Mg<sub>1-x</sub>Fe<sub>x</sub>)O undergoes a high-spin (S = 2) to low-spin (S = 0) transition at ∼45 GPa, accompanied by anomalous changes of this mineral's physical properties, while the intermediate-spin (S = 1) state has not been observed. In this work, we investigate (Mg<sub>1-x</sub>Fe<sub>x</sub>)O (x ≤ 0.25) up to 1.8 TPa via first-principles calculations. Our calculations indicate that (Mg<sub>1-x</sub>Fe<sub>x</sub>)O undergoes a simultaneous structural and spin transition at ∼0.6 TPa, from the B1 phase low-spin state to the B2 phase intermediate-spin state, with Fe's total electron spin S re-emerging from 0 to 1 at ultrahigh pressure. Upon further compression, an intermediate-to-low spin transition occurs in the B2 phase. Depending on the Fe concentration (x), metal-insulator transition and rhombohedral distortions can also occur in the B2 phase. These results suggest that Fe and spin transition may affect planetary interiors over a vast pressure range.