XAS at high pressure for phase diagrams and liquid compressibility: XAS Journal Club, Silvia Boccato

Title: XAS at high pressure for the determination of phase diagrams and liquid compressibility Speaker: Silvia Boccato (Sorbonne University) Abstract: Thanks to its atomic and electronic structure sensitivity, X-ray absorption spectroscopy (XAS) is a very powerful probe to detect structural and chemical modifications driven by pressure and temperature. In particular, XAS properties can be exploited for the determination of melting curves and compressibility of liquids, as well as for the determination of the position of the eutectic point in temperature and composition. These three applications are not only interesting for fundamental reasons, but have very strong implications for the study of planetary interiors as for constraining planets temperature profiles, modeling their internal structure and understanding their crystallization regime. In this talk I will present several case studies in the pressure and temperature range of 10 - 150 GPa and 1500 - 4000 K. First I will focus on the determination of melting curves of 3d metals and 3d metals alloys [1]–[4]. Then, I will show the first example of compressibility determination by XAS in liquid metals under extreme conditions (Ni and Co [5]). Finally, I will present how we exploited XAS to determine the eutectic composition for iron bearing binary systems (Fe-X, X= C, O, S, Si [4]). Reading: [1] G. Morard et al., “Solving Controversies on the Iron Phase Diagram Under High Pressure,” Geophys. Res. Lett., vol. 45, no. 20, pp. 74–82, Oct. 2018. [2] S. Boccato et al., “The Melting Curve of Nickel Up to 100 GPa Explored by XAS,” J. Geophys. Res. Solid Earth, vol. 122, no. 12, pp. 9921–9930, Dec. 2017. [3] R. Torchio et al., “Melting Curve and Phase Relations of Fe-Ni Alloys: Implications for the Earth’s Core Composition,” Geophys. Res. Lett., vol. 47, no. 14, pp. 1–7, 2020. [4] S. Boccato et al., “Melting properties by X ‑ ray absorption spectroscopy : common signatures in binary Fe – C , Fe – O , Fe – S and Fe – Si systems,” Sci. Rep., pp. 1–13, 2020. [5] S. Boccato et al., “Compression of liquid Ni and Co under extreme conditions explored by x-ray absorption spectroscopy,” Phys. Rev. B, vol. 100, no. 18, p. 180101, Nov. 2019.