2022 Fiscal Year Annual Research Report
Constraining Earth's Lower Mantle Point Defect Chemistry from the Charge Disproportionation of Iron
| Project/Area Number |
20K14580
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| Research Institution | Ehime University |
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Principal Investigator |
RITTERBEX S 愛媛大学, 地球深部ダイナミクス研究センター, 特定研究員 (00791782)
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | Grain boundaries / Ferropericlase / Mechanical behavior / Earth's mantle / Super-Earth exoplanets / Iron partitioning |
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| Outline of Annual Research Achievements |
This project aimed investigating the relation between crystal chemistry, lattice defects and the mechanical behavior of ferropericlase. We carried out atomistic simulations based on the density functional theory, conducted on Type I and II subsystems of the Information Technology Center at Nagoya University.
Results show iron to prefer specific grain boundary sites affecting the pressure-induced spin transition and grain boundary partitioning of iron. With those data, ideal shear strengths were determined. It has been shown that high-angle grain boundary motion is particularly accommodated by either shear-coupled migration or grain boundary sliding. The mechanical strengths were found to strongly vary with pressure resulting in grain boundary hardening and weakening across a broad pressure range. By considering the influence of iron spin state on grain boundary migration, we have shown that ferrous iron has a non-unique effect on the criticial shear strength of grain boundaries. In the mantle of super-Earth exoplanets, significant grain boundary weakening is observed to occur, providing a new mechanism of enhanced ductility with depth.
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