Stability, Phase Transitions, Conductivity of MgO₂ near Earth’s mantle Conditions

Magnesium oxide (MgO) is an important mineral in Earth’s mantle. Under oxygen-rich conditions of the mantle, superoxides such as MgO₂ may become stable and influence planetary composition and thermal evolution. Previous crystal structure searches predicted MgO₂ stability above about 116 GPa up to around 600 GPa [1], while static compression experiments observed stability above about 96 GPa and 2150 K [2]. In this work, we investigate the temperature-dependent dynamical stability of cubic and tetragonal MgO₂ at about 100 GPa using density functional theory molecular dynamics (DFT-MD) and phonon calculations. DFT-MD simulations indicate that the tetragonal phase has a higher melting temperature than the cubic phase. Finite-temperature phonon spectra show that the cubic phase becomes dynamically unstable, while the tetragonal phase remains stable. Our ongoing work aims to identify the cubic-to-tetragonal transition mechanism and evaluate electrical and thermal conductivity of the tetragonal phase of MgO₂. These results will provide new insight into oxygen storage and heat transport in deep interiors of Earth and super-Earths.

References:

1. 1. Zhu, Oganov, Lyakhov, Phys. Chem. Chem. Phys., 2013,15, 7696-7700.

           2. Lobanov et al. Scientific Reports 5, 13582 (2015).