<i>Ab initio</i> investigation of post-PPV transitions in MgGeO₃ and NaMgF₃

We present an ab initio investigation of the pressure induced behavior of MgGeO₃ and NaMgF₃, traditional low-pressure analogs (LPAs) of MgSiO₃. The latter undergoes post-post-perovskite (post-PPV) transitions which are exceedingly important in planetary sciences, but at very high pressures of >~500 GPa [1-3]. Although neither MgGeO₃ nor NaMgF₃ are perfect LPAs of MgSiO₃, in overall both display similar dissociation and recombination transitions and the novel types of phases displayed by MgSiO₃ but at much lower pressures easily achievable in diamond anvil cells. Both systems also confirm the ultimate tendency of MgSiO₃ toward the dissociation into its elementary binaries, i.e., AX and BX₂. We also predict potential metastable phase transitions that may occur more easily than dissociation/recombination reactions under insufficiently heated compression.

[1] S. Q. Wu et al., J. Phys.: Condens. Matter, 26, 035402 (2014).
[2] H. Niu et al., Scientic Reports 5, 18347 (2015).
[3] K. Umemoto et al., Earth Planet. Sci. Lett. 478, 40-45 (2017).