Combined in situ synchrotron X-ray diffraction and ultrasonic interferometry study of ϵ-FeSi at high pressure

Ultrasonic interferometry was used in combination with synchrotron X-radiation to determine the compressional and shear wave velocities and unit-cell volumes of ϵ-FeSi (cubic B20 structure) at room temperature and pressures up to 12 GPa. The data collected during compression are compared with those collected during decompression after heating to release stress within the sample cell. By fitting all of the decompression unit-cell volume and sound velocity data to third-order finite-strain equations, we obtain the adiabatic zero-pressure bulk and shear moduli and their first pressure derivatives: K _S0=169.3 (8) GPa, G ₀=116.3 (4) GPa, K′_S0=6.5(3), G′₀=3.0(1). The bulk modulus obtained from this study is in good agreement with those of some previous experimental studies, but significantly lower than those obtained by first-principle calculations. This study presents the first direct measurement on the shear properties of this phase.

Keywords

• mineral physics,
• ultrasonic interferometry,
• equation of state,
• iron silicide,
• elastic properties