Structure determination of liquid Fe alloys at high pressure

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K13644
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Japan Synchrotron Radiation Research Institute
• Principal Investigator: Saori Kawaguchi 公益財団法人高輝度光科学研究センター, 回折・散乱推進室, 研究員 (00773011)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 液体鉄合金 / 地球外核 / ダイヤモンドアンビルセル / 高圧実験 / X線回折 / XANES

Outline of Final Research Achievements

The physical properties are controlled by the atomic correlation, that is, the structure of liquid iron alloys in the Earth’s outer core must be the key to understand the thermal dynamics and evolution of the Earth. Here, I launched the PDF analysis of liquid iron-sulfur alloys in a diamond anvil cell using total X-ray scattering. From the present result, I determined the density of liquid Fe47Ni28S25. The results indicate that S increases the volume change when Fe alloys are melted. It would attributed to the melting of Fe46.5Ni28.5S25 was possibly a result of large anisotropy in the direction of the thermal vibration of the Fe3S structure (space group: (I-4)) compared with face-centered cubic and hexagonal close-packed Fe from XRD data of solid. X-ray absorption spectroscopy measurements were carried out to confirm the structural transition of the liquid iron-sulfur alloy between 10 and 15 GPa, and to suggest that the structural transition may occur at 40 GPa as well.

Free Research Field

高圧地球科学

Academic Significance and Societal Importance of the Research Achievements

地球外核を構成する液体鉄合金について、その測定の困難さから、構造の解明は未だフロンティア的研究でありつづけるテーマである。また、地球外核に相当する高圧下における密度測定例は未だ少なく、地球科学最大の謎の一つである外核の組成についての議論に終止符を打つためにも、鉄硫黄合金の密度データ、ならびに構造情報の解明は必要不可欠である。また、分野を問わず、ダイヤモンドアンビルセルを用いた高圧下における液体・非晶質物質のPDF解析の需要は高い。地球科学分野のみならず、学術的意味を有する重要な研究である。