Prediction of a temperature-induced phase transition in Mg₂GeO₄ by first principles

Here we present a first principles prediction of a temperature-induced phase transition in I-42d-type Mg₂GeO₄, a low-pressure analog [1] of ultrahigh pressure phase of Mg₂SiO₄ [2]. The latter was predicted to occur as a product of dissociation/recombination transitions in MgSiO₃ post-perovskite at multi-Mbar pressures (post-PPV transitions) [3]. In the Mg-Ge-O system, this post-PPV phase occurs beyond ~150 GPa [1]. This new phase transition predicted here alters the sequence of post-PPV phases in Mg₂GeO₄ at high temperatures (>~2,000 K) and likely also in Mg₂SiO₄. I-42d-type Mg₂SiO₄ is predicted to occur in the deep interiors of super-Earths [2-5]. Therefore, this newly found phase transition should be relevant for modeling the internal dynamics and structure of super-Earth-type planets.

[1] K. Umemoto and R. M. Wentzcovitch, Phys. Rev. Materials 3, 123601
(2019).
[2] S. Q. Wu et al., J. Phys.: Condens. Matter, 26, 035402 (2014).
[3] K. Umemoto et al., Earth Planet. Sci. Lett. 478, 40-45 (2017).
[4] H. Niu et al., Scientific Reports 5, 18347 (2015).
[5] A. van den Berg, et al. Icarus 317, 412-426 (2019).