The FeSi phase diagram to 150 GPa

The melting curve of FeSi has been determined to 150 GPa in the laser-heated diamond anvil cell (LH-DAC) on the basis of discontinuities in the power versus temperature function. A multianvil experimental cross-check at 12 GPa using textural criteria as a proxy for melting is in good agreement with our LH-DAC results. The melting point of FeSi reaches similar to 4000 K at the core mantle boundary and an extrapolated value of 4900 K at the inner-core boundary (ICB). We also present the melting curve as determined by the Lindemann melting law; this agrees well with our experimental curve to 70 GPa and then diverges to higher temperatures, reaching 6200 K at the ICB. These temperatures are substantially higher than previous LH-DAC determinations. The boundary of the epsilon-FeSi -> CsCl-FeSi subsolidus transition has also been determined by synchrotron-based X-ray diffraction at high pressures, and the results confirm a negative Clapeyron slope for the transition. We conclude that if present, FeSi is likely to be solid within the D '' layer and is unlikely to be present within the inner core for any plausible bulk core silicon content.