Title: Ultrahigh-pressure disordered eight-coordinated phase of Mg2GeO4: Analogue for super-Earth mantles

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America
 [1];  [2]; ORCiD logo [2]; ORCiD logo [2]; ORCiD logo [2];  [2];  [3];  [4];  [4];  [5];  [5]; ORCiD logo [6]
  1. Carnegie Inst. of Science, Washington, DC (United States); Princeton Univ., NJ (United States)
  2. Carnegie Inst. of Science, Washington, DC (United States)
  3. Univ. of Nevada, Las Vegas, NV (United States)
  4. Argonne National Lab. (ANL), Argonne, IL (United States)
  5. Univ. of Chicago, IL (United States)
  6. Princeton Univ., NJ (United States)
+ Show Author Affiliations

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 $$I\bar{4}2d$$ structure indistinguishable from $$I\bar{4}3d$$ 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.

Research Organization:
Argonne National Laboratory (ANL)
Sponsoring Organization:
National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC)
Grant/Contract Number:
AC02-06CH11357; FG02-94ER14466
OSTI ID:
1906378
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 8 Vol. 119; ISSN 0027-8424
Publisher:
National Academy of SciencesCopyright Statement
Country of Publication:
United States
Language:
English

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58 GEOSCIENCES
order-disorder transition
post-postperovskite
super-Eat mineralogy