Synthesis and Compression study of orthorhombic $Fe_7(C,Si)_3$: A possible constituent of the Earth's core

Abstract

The orthorhombic phase of Si-doped Fe carbide is synthesized at high pressures and temperatures using laser-heated diamond anvil cell (LHDAC), followed by its characterization using X-ray diffraction (XRD) measurements, Transmission Electron Microscopy (TEM), and Raman spectroscopy. High-pressure XRD measurements are carried out up to about 104 GPa at room temperature for determination of the equation of state (EOS) parameters of the synthesized sample. No evidence of structural transition is observed, though two anomalies are found in the compression behaviour of our sample at about 28 and 78 GPa, respectively. Pressure evolution of isothermal bulk modulus shows elastic stiffening around 28 GPa followed by softening around 78 GPa. These anomalies are possibly related to two different magnetic transitions driven by pressure-induced anisotropic strain in the unit cell. Extrapolation of the density profile of our study to the inner core conditions agrees very well with PREM data with an uncertainty of about 3-4%. We have estimate bulk modulus value seems to be 8-9% less than that of PREM data in the shown pressure range and is best matched in comparison to other reported values for the non-magnetic phase.