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

The vibrational and structural properties of a hydrogen-rich group IVa hydride, Ge(CH sub(3)) sub(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 sub(1)/c for phase III, and P2 sub(1) for phase IV, respectively. These transitions are suggested to result from the changes in the inter- and intramolecular bonding of this compound. The softening of some Raman modes on CH sub(3) groups and their sudden disappearance indicate that Ge(CH sub(3)) sub(4) might be an ideal compound to realize metallization and even high-temperature superconductivity at modest static pressure for laboratory capability.