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

本计画旨在探讨铁方镁石的晶体化学、晶格缺陷与力学行为之间的关系。我们进行了原子模拟的基础上的密度泛函理论，在名古屋大学的信息技术中心的I型和II型子系统进行。结果表明，铁更喜欢特定的晶界网站影响的压力诱导自旋转变和晶界铁的分区。根据这些数据，确定了理想的剪切强度。它已被证明，高角度晶界运动是特别容纳的剪切耦合迁移或晶界滑动。的机械强度被发现强烈的变化与压力，导致在晶界硬化和削弱在一个广泛的压力范围。通过考虑铁的自旋状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是非唯一的。在超地球系外行星的地幔中，观察到发生了显着的晶界弱化，提供了一种新的机制，即随着深度的增加，韧性增强。

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.