Effects of Si on the elastic property of Fe at Earth's inner core pressures: First principles study

Abstract

We investigate the effects of silicon incorporation on the structural stability and elasticity of iron at the Earth's inner core pressures by means of the density functional calculation method in order to clarify the acceptability of silicon to the possible light elements dissolving in the inner core. Calculations show that (1) silicon incorporation enhances the bcc stability field as experimental understandings but hcp phase is the most stable at the inner core pressures even in Fe 0.875Si 0.125, (2) silicon less affects to the elasticity of bcc iron but decreases shear moduli of hcp and fcc phases, (3) it does not drastically change the elastic wave velocities of iron due to the cancellation of associated changes in density and elastic moduli, (4) both P and S wave velocities for each phase and compound linearly depend on the density, and (5) fcc phase is more elastically anisotropic than hcp phase and the anisotropy is enhanced by silicon. We apply two different high-temperature corrections to the wave velocities. Inner core P-wave velocity is well reproduced in the both models, whereas the calculated S-wave velocities significantly depend on the temperature correction. Small effects of silicon on the density–velocity relations are found in both models.