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

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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.