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

Abstract

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 $\mathit{Pa}$-3 for phase I, Pnma for phase II, $P$2${}_{1}$/$c$ for phase III, and $P$2${}_{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${}_{3}$ 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.