Germanates are often used as structural analogs of planetary silicates. We
have explored the high-pressure phase relations in Mg2GeO4 using diamond anvil
cell experiments combined with synchrotron x-ray diffraction and computations
based on density functional theory. Upon room temperature compression,
forsterite remains stable up to 30 GPa. At higher pressures, a phase transition
to a CmC21 structure was observed, which remained stable to the peak pressure
of 105 GPa. Using a 3rd order Birch Murnaghan fit to the experimental data, we
obtained V0 = 305.1 (3) A3, K0 = 124.6 (14) GPa and K' = 3.86 (fixed) for
forsterite and V0 = 263.5 (15) A3, K0 = 175 (7) GPa and K' = 4.2 (fixed) for
the CmC21 phase. In three separate runs, the forsterite sample was compressed
to 26 GPa, 54 GPa and 105 GPa respectively and then laser-heated to ~2500 K. On
laser heating, a mixture of perovskite MgGeO3 + MgO was found to be stable at
the lower pressure conditions, whereas post-perovskite + MgO was observed at
the highest pressure