Constraining Earth's Lower Mantle Point Defect Chemistry from the Charge Disproportionation of Iron

本项目旨在研究方镁铁石的晶体化学、晶格缺陷和力学行为之间的关系。基于密度泛函理论，对名古屋大学信息技术中心的I类和II类子系统进行了原子模拟，结果表明，铁优先选择特定的晶界位置，影响铁的压力诱导自旋转变和晶界分配。根据这些数据，确定了理想的抗剪强度。研究表明，大角度晶界运动特别适合于剪切耦合迁移或晶界滑动。在较宽的压力范围内，力学强度随压力变化强烈，导致晶界硬化和弱化。通过考虑铁的自旋态对晶界迁移的影响，我们证明了亚铁对晶界临界剪切强度的影响不是唯一的。在超地系外行星的地幔中，观察到明显的晶界弱化，提供了一种新的增韧机制。

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.