Spectroscopic X-ray and Mössbauer Characterization of M 6 and M 5 Iron(Molybdenum)-Carbonyl Carbide Clusters: High Carbide-Iron Covalency Enhances Local Iron Site Electron Density Despite Cluster Oxidation

McGale, Jeremy; Cutsail, George E.; Joseph, Chris; Rose, Michael J.; DeBeer, Serena

doi:10.1021/acs.inorgchem.9b01870

Abstract

We conducted shock wave experiments on iron carbide Fe₃C up to a Hugoniot pressure of 245 GPa. The correlation between the particle velocity (u_p) and shock wave velocity (u_s) can be fitted into a linear relationship,u_s= 4.627(±0.073) + 1.614(±0.028)u_p. The density‐pressure relationship is consistent with a single‐phase compression without decomposition. The inference is further supported by the comparison of the observed Hugoniot density with the calculated Hugoniot curves of possible decomposition products. The new Hugoniot data combined with the reported 300‐K isothermal compression data yielded a Grüneisen parameter ofγ= 2.23(7.982/ρ)^0.29. The thermal equation of state of Fe₃C is further used to calculate the density profile of Fe₃C along the Earth's adiabatic geotherm. The density of Fe₃C was found to be too low (by ~5%) to match the observed density in the Earth's inner core, and Fe₃C is unlikely a dominant component of the inner core.

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