FIRST–PRINCIPLES CALCULATIONS OF THE STATE EQUATIONS AND RELATIVE STABILITY OF IRON CARBIDES AT THE EARTH’S CORE PRESSURES
K.D. Litasov1,2, Z.I. Popov3, P.N. Gavryushkin1,2, S.G. Ovchinnikov4,5,6, A.S. Fedorov4,5,6
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 2, Novosibirsk, 630090, Russia
3L.V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Akademgorodok, 50, Building 38, Krasnoyarsk, 660036, Russia Novosibirsk
4L.V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, pr. Svobodnyi 79, Krasnoyarsk, 660041, Russia
5Siberian Federal University, pr. Svobodnyi 79, Krasnoyarsk, 660041, Russia
6Siberian Federal University
Keywords: Iron carbide, Earth’s core, first-principles (or quantum-chemical) calculations, density, bulk modulus, magnetic moment
Abstract
Recent experimental studies have demonstrated that Fe
3C is more stable than Fe
7C
3 under PT -conditions of the Earth’s core. Theoretical calculations at 0 K, in turn, show the possible stability of Fe
2C at the core pressures. Therefore, a theoretical modeling of iron carbides at ≤500 GPa is carried out. Energetically stable phases and the pressures of magnetic transitions at 0 K are determined. The parameters of magnetic transitions for Fe
7C
3 and Fe
3C are consistent with those determined in the previous papers. The phase transition from Pnnm to Pnma in Fe
2C at 28 GPa is estimated. At >100 GPa, Fe
2C loses its magnetic moment. Assuming carbon to be the only light element in the system, the first-principles calculations yield 2.7-2.9 and 2.0-2.2 wt.% C at the boundary of the inner core at 5000 and 7000 K, respectively.
DOI: http://dx.doi.org/10.1016/j.rgg.2015.01.010
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