Host: The Mineralogical Society of Japan
Stable phase and equation of state of iron-silicon alloys, Fe-8.7 wt.% Si and Fe-17.8 wt.% Si, have been investigated using diamond-anvil cell techniques up to 196 GPa and 124 GPa, respectively. The unit cell volumes at room temperature were measured by X-ray diffraction method using synchrotron radiation and an imaging plate (IP). Fe-8.7 wt.% Si transformed from bcc phase into the bcc and hcp phases at 16 GPa and room temperature, and the phase transformation to the hcp phase was completed at 36 GPa. The high-pressure phase of Fe-8.7 wt.% Si with hcp structure was stable up to 196 GPa. No phase transition in bcc-Fe-17.8 wt.% Si was observed up to 124 GPa. The pressure-volume data were fitted to a third-order Birch-Murnaghan equation of state (BM EOS) with zero-pressure parameters: V0 = 22.2(8) A3, K0 = 198(9) GPa, and K'0 = 4.7(3) for hcp-Fe-8.7 wt.% Si and V0 = 179.41(45) A3, K0 = 207(15) GPa and K'0 = 5.1(6) for Fe-17.8 wt.% Si. The density and bulk sound velocity of hcp-Fe-8.7 wt.% Si indicate that the inner core would contain a few weight % of Si.
