Structural, spin, and metal–insulator transitions of (Mg,Fe)O at ultrahigh pressure

  • Event Date: 2021-11-22
  • Computational quantum materials
  • Speaker: Prof. Han Hsu  /  Host: Prof. Feng-Chuan Chuang
    Place: Online Seminar

Title: Structural, spin, and metal–insulator transitions of (Mg,Fe)O at ultrahigh pressure

Time: 15:10-16:10, Monday, 2021/11/22

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Fe-bearing MgO [(Mg,Fe)O] is a major constituent of the Earth’s lower mantle; it is also believed to be a major constituent of terrestrial exoplanets, where the pressure can reach to the tera-Pascal (TPa) range. In the Earth’s lower mantle (pressure range 23–135 GPa), (Mg,Fe)O crystallizes in the B1 (NaCl-type) structure and undergoes a high-spin (HS, S = 2) to low-spin (LS, S = 0) transition at ∼45 GPa, accompanied by anomalous changes of this mineral’s physical properties, while the intermediate-spin (IS, S = 1) state has not been observed. Experiments have shown that B1 MgO transforms into the B2 (CsCl-type) structure at ~0.5 TPa, but the behavior of Fe and its effects on B2 MgO at ultrahigh pressure remain unknown. In this work, we investigate (Mg,Fe)O up to 1.8 TPa via first-principles calculations. Our calculations indicate that (Mg,Fe)O undergoes a simultaneous structural and spin transition at ∼0.6 TPa, from the B1 phase LS state to the B2 phase IS state, with Fe’s total electron spin (S) re-emerging from 0 to 1 at ultrahigh pressure. Upon further compression, an IS–LS spin transition occurs in the B2 phase. Depending on the Fe concentration, 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.