PHASE RELATIONS OF IRON CARBIDES Fe2C, Fe3C, AND Fe7C3 AT THE EARTH’S CORE PRESSURES AND TEMPERATURES
N.E. Sagatov1,2, P.N. Gavryushkin1,2, I.V. Medrish3,4, T.M. Inerbaev1,5, K.D. Litasov6,7
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 1, Novosibirsk, 630090, Russia
3International Research Center for Theoretical Materials Science, Samara State Technical University, ul. Molodogvardeiskaya 244, Samara, 443100, Russia
4Samara Center for Theoretical Materials Science, Samara National Research University, ul. Akademika Pavlova 1, Samara, 443011, Russia
5L.N. Gumilyov Eurasian National University, ul. Satbaeva 2, Astana, 010008, Kazakhstan
6Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Kaluzhskoe sh. 14, Troitsk, Moscow, 108840, Russia
7Fersman Mineralogical Museum, Russian Academy of Sciences, Leninskii pr. 18/2, Moscow, 119071, Russia
Keywords: Iron carbides, USPEX, AIRSS, crystal structure prediction, quasi-harmonic approximation
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.
DOI: 10.15372/RGG2019146
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