[S-IT17] TRANSPORT PROPERTIES AND PROCESSES IN THE EARTH

[SIT17-11] Different structural behavior of MgSiO₃ and CaSiO₃ glasses at high pressures

*Nozomi Kondo^1,2, Yoshio Kono¹, Itaru Ohira³, Rostislav Hrubiak⁴, Koji Ohara⁵, Kiyofumi Nitta⁵, Oki Sekizawa⁵ (1.Geodynamics Research Center, Ehime University, 2.Institute for Planetary Materials, Okayama University, 3.Department of Chemistry, Gakushuin University, 4.High Pressure Collaborative Access Team, X-ray Science Division, Argonne National Laboratory, 5.SPring-8 synchrotron facility, Japan Synchrotron Radiation Research Institute)

Keywords:glass structure, MgSiO3, CaSiO3, pair distribution function, high pressure

Knowledge of the structural behavior of silicate melts and/or glasses at high pressures provide fundamental information in discussing the nature and properties of silicate magmas in the Earth’s interior. The behavior of Si-O structure under high pressure conditions has been widely studied, while the effect of cation atoms on the high-pressure structural behavior of silicate melts or glasses has not been well investigated. In this study, we investigated the structures of MgSiO₃ and CaSiO₃ glasses up to ~5 GPa by in-situ X-ray pair distribution function measurements, to understand the effect of different cations (Mg²⁺ and Ca²⁺) on high pressure structural behavior of silicate glasses. We found that the structural behaviors of MgSiO₃ and CaSiO₃ glasses are different at high pressures. The structure of MgSiO₃ glass changes by shrinking of Si-O-Si angle with increasing pressures, which is consistent with previous studies for SiO₂ and MgSiO₃ glasses. On the other hand, CaSiO₃ glass shows almost no change in Si-Si distance at high pressures, while the intensities of two peaks at ~3.0 Å and ~3.5 Å change with increasing pressure. The structural change in CaSiO₃ glass at high pressure is interpreted as the change of the fraction of the edge-shared and corner-shared CaO₆-SiO₄ structures. The different high-pressure structural behavior obtained in MgSiO₃ and CaSiO₃ glasses may be structural origin of the difference in the properties such as viscosity of MgSiO₃ and CaSiO₃ melts at high pressures, implying importance of the different structural behavior due to different cation atoms to discuss the nature and properties of silicate magmas in the Earth’s interior.