Ab initioprediction of an order-disorder transition inMg2GeO4: Implication for the nature of super-Earth's mantles,Physical Review Materials

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Ab initioprediction of an order-disorder transition inMg2GeO4: Implication for the nature of super-Earth's mantles
Physical Review Materials ( IF 3.1 ) Pub Date : 2021-09-08 , DOI: 10.1103/physrevmaterials.5.093604
Koichiro Umemoto _{1,

2} , Renata M. Wentzcovitch _{3,

4}

Affiliation

Here we present an ab initio prediction of an order-disorder transition (ODT) from a

I \bar{4} 2 d

-type to

{Th}_{3} P_{4}

-type phase in the cation sublattices of

{Mg}_{2} Ge O_{4}

, a post-post-perovskite phase. This uncommon type of prediction is achieved by carrying out a high-throughput sampling of atomic configurations in a 56-atom supercell followed by a Boltzmann ensemble statistics calculation.

{Mg}_{2} Ge O_{4}

is a low-pressure analog of

I \bar{4} 2 d

-type

{Mg}_{2} Si O_{4}

, a predicted major planet-forming phase of super-Earths' mantles. Therefore, a similar ODT is anticipated in

I \bar{4} 2 d

-type

{Mg}_{2} Si O_{4}

as well, which should impact the internal structure and dynamics of these planets. The prediction of this

{Th}_{3} P_{4}

-type phase in

{Mg}_{2} Ge O_{4}

further enhances the relationship between the crystal structures of Earth/planet-forming silicates and oxides at extreme pressures and those of rare-earth sesquisulfides at low pressures.

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