@article{
doi:10.1073/pnas.2114424119,
author = {Rajkrishna Dutta  and Sally June Tracy  and R. E. Cohen  and Francesca Miozzi  and Kai Luo  and Jing Yang  and Pamela C. Burnley  and Dean Smith  and Yue Meng  and Stella Chariton  and Vitali B. Prakapenka  and Thomas S. Duffy },
title = {Ultrahigh-pressure disordered eight-coordinated phase of {Mg$_2$GeO$_4$}: Analogue for super-Earth mantles},
journal = {Proceedings of the National Academy of Sciences},
volume = {119},
number = {8},
pages = {e2114424119},
year = {2022},
doi = {10.1073/pnas.2114424119},
URL = {https://www.pnas.org/doi/abs/10.1073/pnas.2114424119},
eprint = {https://www.pnas.org/doi/pdf/10.1073/pnas.2114424119},
abstract = {Mg2GeO4 is important as an analog for the ultrahigh-pressure behavior of Mg2SiO4, a major component of planetary interiors. In this study, we have investigated magnesium germanate to 275 GPa and over 2,000 K using a laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction and density functional theory (DFT) computations. The experimental results are consistent with the formation of a phase with disordered Mg and Ge, in which germanium adopts eightfold coordination with oxygen: the cubic, Th3P4-type structure. DFT computations suggest partial Mg-Ge order, resulting in a tetragonal I4¯2d structure indistinguishable from I4¯3d Th3P4 in our experiments. If applicable to silicates, the formation of this highly coordinated and intrinsically disordered phase may have important implications for the interior mineralogy of large, rocky extrasolar planets.}}