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High-pressure phases of a hydrogen-rich compound: tetramethylgermane

The vibrational and structural properties of a hydrogen-rich Group IVa hydride, Ge(CH$_3$)$_4$, are studied by combining Raman spectroscopy and synchrotron X-ray diffraction measurements at room temperature and at pressures up to 30.2 GPa. Both techniques allow the obtaining of complementary information on the high-pressure behaviors and yield consistent phase transitions at 1.4 GPa for the liquid to solid and 3.0, 5.4, and 20.3 GPa for the solid to solid. The four high-pressure solid phases are identified to have the cubic, orthorhombic, monoclinic and monoclinic crystal structures with space groups of Pa-3 for phase I, Pnma for phase II, P2$_1$/c for phase III, and P2$_1$ for phase IV, respectively. These transitions are suggested to result from the changes in the inter- and intra-molecular bonding of this compound. The softening of some Raman modes on CH$_3$ groups and their sudden disappearance indicate that Ge(CH$_3$)$_4$ might be an ideal compound to realize metallization and even high-temperature superconductivity at modest static pressure for laboratory capability.