The equation of state of CsCl-structured FeSi to 40 GPa: Implications for silicon in the Earth's core

We have measured the compressibility of CsCl-structured FeSi to 40 GPa by X-ray powder diffraction using synchrotron radiation. A third order Birch-Murnaghan equation of state fit to the experimental data yields V-0=21.74+/-0.02 Angstrom, with a K-0 of 184+/-5 GPa and K'(0)=4.2+/-0.3. The measured density and elastic properties of CsCl-FeSi are consistent with silicon being a major element in the Earth's core.