Ultrahigh-pressure disordered eight-coordinated phase of Mg<sub>2</sub>GeO<sub>4</sub>: Analogue for super-Earth mantles.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 35165195.
- Also identified by DOI 10.1073/pnas.2114424119 and PMC identifier 8872715.
- Licence recorded as CC BY-NC-ND.
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Abstract
Mg<sub>2</sub>GeO<sub>4</sub> is important as an analog for the ultrahigh-pressure behavior of Mg<sub>2</sub>SiO<sub>4</sub>, 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, Th<sub>3</sub>P<sub>4</sub>-type structure. DFT computations suggest partial Mg-Ge order, resulting in a tetragonal [Formula: see text] structure indistinguishable from [Formula: see text] Th<sub>3</sub>P<sub>4</sub> 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.