First‐principles prediction of Si‐doped Fe carbide as one of the possible constituents of Earth's inner core. Issue 17 (9th September 2017)

• Record Type: Journal Article
• Authors: Das, Tilak; Chatterjee, Swastika; Ghosh, Sujoy; Saha‐Dasgupta, Tanusri
• Is Part Of: Geophysical research letters. Volume 44:Issue 17(2017)
• Page Start: 8776
• Page End: 8784
• Publication Date: 2017-09-09
• Subjects: light elements -- inner core -- carbon -- silicon -- Fe7C3 -- Earth's interior: composition and state, core processes, core; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL073545
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We perform a computational study based on first‐principles calculations to investigate the relative stability and elastic properties of the doped and undoped Fe carbide compounds at 200–364 GPa. We find that upon doping a few weight percent of Si impurities at the carbon sites in Fe7 C3 carbide phases, the values of Poisson's ratio and density increase while V P, and V S decrease compared to their undoped counterparts. This leads to marked improvement in the agreement of seismic parameters such as P wave and S wave velocity, Poisson's ratio, and density with the Preliminary Reference Earth Model (PREM) data. The agreement with PREM data is found to be better for the orthorhombic phase of iron carbide (o‐Fe7 C3 ) compared to hexagonal phase (h‐Fe7 C3 ). Our theoretical analysis indicates that Fe carbide containing Si impurities can be a possible constituent of the Earth's inner core. Since the density of undoped Fe7 C3 is low compared to that of inner core, as discussed in a recent theoretical study, our proposal of Si‐doped Fe7 C3 can provide an alternative solution as an important component of the Earth's inner core. Key Points: The elastic properties of the Si‐doped and undoped Fe7 C3 are calculated at inner core conditions using first‐principles calculations Si‐doped orthorhombic Fe7 C3 provides good agreement with the PREM data Crystallization of Si‐doped Fe7 C3 from a liquid outer core with ~1 wt % carbon may be possible if silicon is included in the core