Collaborative Research: Theoretical and Experimental Investigations on the Role of Iron in the Physics and Chemistry of the Lower Mantle

地球的下地幔占地球质量和体积的一半以上。它的组成、性质和动力学取决于组成相的晶体化学和矿物物理性质，主要是硅酸盐钙钛矿、后钙钛矿和铁方长石。铁是这些相中的主要或次要元素。铁的电子结构，包括它的价态、位占用和电子自旋态，可能对宿主相的状态方程、元素分配和输运性质有重要影响。最近对含铝钙矿和铁长石中铁的自旋态的研究表明，在下地幔条件下，铁的自旋态发生了剧烈的变化。这些新发现的自旋变化对下地幔性质的影响是地球物理学需要进一步研究的重要挑战。作为第一步，有必要确定正在发生的自旋变化以及它们如何与铁环境和价相耦合。摩根教授和李教授正在结合从头算能量学、热力学建模和Mössbauer实验来研究地幔矿物中铁的电子结构如何随压力和温度变化。特别地，他们在低地幔压力、温度和组成条件下研究了钙钛矿和后钙钛矿相中铁的位置占用、价态和自旋态。

The Earth¹s lower mantle accounts for more than half of the mass and volume of the planet. Its composition, properties and dynamics depend on the crystal chemistry and mineral physics of the component phases, mainly silicate perovskites, postperovskite, and ferropericlase. Iron is a major or minor element in these phases. The electronic structure of iron, including its valence state, site occupancy, and electronic spin state, may have significant influence on the equation-of-state, element partitioning, and transport properties of the host phases. Recent investigations on the spin state of iron in aluminum-bearing perovksite and ferropericlase revealed dramatic spin changes under lower mantle conditions. The impact of these newly identified spin changes on lower mantle properties is an important challenge for geophysics requiring significant further research. As a first step, it is necessary to identify the spin changes that are occurring and how they couple to iron environment and valence. Professors Morgan and Li are combining ab initio based energetics, thermodynamic modeling, and Mössbauer experiments to investigate how the electronic configuration of iron in mantle minerals changes with pressure and temperature. In particular, they are examining the site occupancy, valence state, and spin state of iron in perovskite and post-perovskite phases under lower mantle pressure, temperature, and composition conditions.