Phase Relations of Iron Carbides Fe2C, Fe3C, and Fe7C3 at the Earth’s Core Pressures and Temperatures

Nursultan E. Sagatov, Pavel N. Gavryushkin, Inna V. Medrish, Талгат Муратович Инербаев, Konstantin D. Litasov

2020

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DOI 10.15372/rgg2019146
Data confidence 70 medium
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Abstract

Abstract —Based on first-principle calculations in the framework of the density functional theory and structure prediction algorithms, we have determined iron carbide phases stable at the Earth’s core pressures and temperatures. It is shown that Fe7C3 is unstable and decomposes into the mixture Fe2C + Fe3C over the entire range of pressures and temperatures specific to the Earth’s inner core. Subsequent decomposition of Fe3C into the mixture Fe + Fe2C is unfavorable. We also predict a new low-temperature modification Fe3C-C2/m-II dynamically and thermodynamically stable over the pressure range 290–305 GPa.