Ultrahigh-pressure disordered eight-coordinated phase of Mg 2 GeO 4 : Analogue for super-Earth mantles

Abstract

Significance This work presents experimental evidence for the formation of a phase with eightfold coordination of germanium by oxygen in Mg 2 GeO 4 , a well-known analogue of Mg 2 SiO 4 at extreme pressure and temperatures. Using both experiments and theoretical computations, we have determined the structure, equation of state, and phase stability of this phase at pressures above 200 GPa. The existence of this phase in the silicate counterpart may play an important role in the structure and dynamics of the deep interiors of large, rocky exoplanets.