Acoustic velocities and thermoelastic properties of FeSi at high P and T

Velocity and density profiles of the Earth's deep interior show a marked discrepancy from pure iron under similar conditions of high pressure and temperature, indicating that the core of the planet must contain some amount of some light element(s). In order to assess which elements these may be, and in what proportions, the physical properties of some iron-light element alloys must be experimentally ascertained under extreme conditions. Among those light elements, Si has been strongly suggested as a possible constituent of the Earth's core, which is primarily supported by current data on bulk sound speed and density derived from static compression; the shear properties on these iron-light element alloys have been rarely investigated at relevant pressure and temperature conditions. Acoustic velocity measurements using ultrasonic interferometry, in conjunction with synchrotron X-radiation techniques at beamline X17B2 of NSLS, Brookhaven National Lab, allow for simultaneous measurements of the bulk and shear elastic properties of these materials at high pressures and temperatures. Using this technique, we have determined the acoustic velocities and elastic properties of ɛ-FeSi at high pressures and temperatures, yielding the first complete and thermodynamically consistent data set of thermoelastic properties (adiabatic bulk and shear moduli, and their pressure and temperature derivatives) for this material. These new data will be presented and used to draw comparisons to seismic profiles of the Earth's core.