[S-IT18] Planetary cores: Structure, formation, and evolution

[SIT18-04] Elastic wave velocity of Fe-Si alloy at high pressure

*Tatsuya Sakamaki¹, Hidenori Terasaki², Yuki Shibazaki¹, Hiromu Tobe¹, Yuta Shimoyama², Yuji Higo³, Akio Suzuki¹ (1.Tohoku University, 2.Osaka University, 3.JASRI)

Keywords:iron-silicon alloy, elastic wave velocity, high pressure

As an approach to understanding planetary cores, a determination of the elastic property of iron-alloys is powerful. Here, we report both of elastic velocity and density of Fe-Si alloy up to 6 GPa and 1873 K using ultrasonic technique combining with synchrotron x-ray at BL04B1 of SPring-8. In this experiment, Fe-10at%Si system showed three phases (bcc, fcc, bcc+fcc) depending on pressure and temperature conditions. This indicated that a stability field of fcc phase is large compared to ambient condition. Based on the velocity measurements, negative temperature effect on the velocity was found clearly. The phase transition from bcc to fcc around 6 GPa and 1000 K caused small changes in properties: the density and velocity (Vp) jump are 1.2% and 0.8%, respectively. Comparing with pure-iron (bcc), the bcc-Fe-Si is 10% faster at the same density. These knowledges can help us to analyze new planetary observations in the near future.