2021/01/31 by Rajkrishna Dutta, Sally J. Tracy, S. J. Tracy +14
Chemistry · Earth and Planetary Sciences · Materials Science · Physics and Astronomy · #Chemistry #Computational chemistry #Condensed matter physics #Crystal Structures and Properties #Crystal structure #Crystallography #Density functional theory #Diamond anvil cell #Diffraction #Geological and Geochemical Analysis #Germanate #Germanium #High-pressure geophysics and materials #Materials science #Optics #Phase (matter) #Physics #Silicon #Synchrotron #Tetragonal crystal system #cond-mat.mtrl-sci #physics.geo-ph
paper · pdf · doi:10.1073/pnas.2114424119
published as PNAS 119 (8) e2114424119 (2022) · 13 pages, 5 figures and 18 pages of Supplementary Material
arxiv created 2021/08/20 · openalex publication_date 2022/02/14 · arxiv updated 2022/03/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Mg2GeO4 is an analogue for the ultra-high pressure behavior of Mg2SiO4, so we have investigated magnesium germanate to 275 GPa and over 2000 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 a novel phase with disordered Mg and Ge, in which germanium adopts eight-fold coordination with oxygen: the cubic Th3P4- type structure. Simulations using the special quasirandom structure (SQS) method suggest partial order in the tetragonal I-42d structure, indistinguishable from I-43d Th3P4 in our experiments. These structures have not been reported before in any oxide. If applicable to silicates, the formation of this highly coordinated and intrinsically disordered phase would have important implications for the interior mineralogy of large, rocky extrasolar planets.