Work

First-principles calculations of properties of orthorhombic iron carbide Fe7C3 at the Earth's core conditions

Year: 2015

Type: article

Abstract: A recently discovered phase of orthorhombic iron carbide o-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$ [Prescher et al., Nat. Geosci. 8, 220 (2015)] is assessed as a potentially important phase for interpretation of the properties of the Earth's core. In this paper, we carry out first-principles calculations on o-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$, finding properties to be in broad agreement with recent experiments, including a high Poisson's ratio (0.38). Our enthalpy calculations suggest that o-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$ is more stable than Eckstrom-Adcock hexagonal iron carbide (h-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$) below approximately 100 GPa. However, at 150 GPa, the two phases are essentially degenerate in terms of Gibbs free energy, and further increasing the pressure towards Earth's core conditions stabilizes h-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$ with respect to the orthorhombic phase. Increasing the temperature tends to stabilize the hexagonal phase at 360 GPa, but this trend may change beyond the limit of the quasiharmonic approximation.

Source: Physical Review B

DOI: 10.1103/physrevb.91.214112

Authors: Zamaan Raza, Nina Shulumba, Nuala M. Caffrey, Leonid Dubrovinsky, Igor A. Abrikosov

Institutions: Linköping University, Saarland University, University of Bayreuth, National University of Science and Technology, National Research Tomsk State University

Language: English

Topic: High-pressure geophysics and materials

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: bronze