1:45 PM - 2:00 PM
[SCG58-01] Effect of Oxygen Vacancies on stability in Al-bearing Bridgmanite based on DFT calculations
Keywords:Bridgmanite, Mineral Physics, Molecular Dynamics, Oxygen Vacancy
Bridgmanite accounts for more than 70% by volume in the lower mantle and is one of the most important minerals in geoscience, having a major effect on the physical properties of the lower mantle. Although the composition of bridgmanite is often assumed to be MgSiO3 to reduce computational cost in theoretical approaches, it is known that bridgmanite does not exist in such a pure composition in the actual lower mantle and that vacancies may be formed by the incorporation of Al and Fe. Experimental results have shown that the higher the pressure, the fewer vacancies are found, and from around 27 GPa, vacancies are almost negligible. Vacancies are believed to have a significant effect on the transport properties and thermo-elastic and viscous properties of minerals, and the boundary region where the vacancy ratio drops sharply is predicted to have a significant change in mineral properties, which may explain the decrease in mantle viscosity and stagnant slabs observed at depths around 1000 km. The study of the effect of vacancies on elastic properties and stability will contribute to our understanding of the composition of the upper part of the lower mantle in comparison with actual seismic observations.
In investigating these physical properties, the ab initiio calculation approach is effective in reproducing the ultrahigh temperature and pressure conditions of the Earth's interior by fixing the density of vacancies more accurately than experimental methods. Until recently, it has been assumed that vacancies are unlikely to exist in the lower mantle region where bridgmanite exists, and the last ab initio study of the properties of bridgmanite containing vacancies was Yamamoto et al. (2003). However, recent experimental studies suggest that vacancies may exist from the top of the lower mantle region to the upper region to the extent that they affect mantle properties.
In this study, we prepared a system similar to the structure used in a previous study by Yamamoto et al. (2003) and investigated the stability and elastic properties of bridgmanite with vacancies by performing molecular dynamics calculations. By incorporating temperature effects, which were not included in Yamamoto et al. (2003), we can consider the effects of the interaction between the vacancies and the high-temperature state on the stability and elastic properties of bridgmanite.
In investigating these physical properties, the ab initiio calculation approach is effective in reproducing the ultrahigh temperature and pressure conditions of the Earth's interior by fixing the density of vacancies more accurately than experimental methods. Until recently, it has been assumed that vacancies are unlikely to exist in the lower mantle region where bridgmanite exists, and the last ab initio study of the properties of bridgmanite containing vacancies was Yamamoto et al. (2003). However, recent experimental studies suggest that vacancies may exist from the top of the lower mantle region to the upper region to the extent that they affect mantle properties.
In this study, we prepared a system similar to the structure used in a previous study by Yamamoto et al. (2003) and investigated the stability and elastic properties of bridgmanite with vacancies by performing molecular dynamics calculations. By incorporating temperature effects, which were not included in Yamamoto et al. (2003), we can consider the effects of the interaction between the vacancies and the high-temperature state on the stability and elastic properties of bridgmanite.