Velocity and Stability of Condensed Polymorphic SiH_4: A High-Temperature High-Pressure Brillouin Investigation

Silane (SiH_4) is a promising hydrogen-rich compound for pursing high temperature superconducting. Previous high pressure measurements of Raman, x-ray diffraction and theoretical studies on SiH_4 mainly focused on its polymorphic structures above 50 GPa, while the structure and the stability under lower pressure range are still unclear. Here we report an investigation of condensed SiH_4 by Brillouin scattering measurements at high temperature up to 407 K and high pressure up to 18 GPa. Brillouin scattering frequencies of fluid SiH_4 under compression are obtained under isothermal conditions of 300 K, 359 K and 407 K. The SiH_4 becomes unstable with increasing temperature and subsequently decomposes into silicon and H_2. We find that compression at room temperature induces two velocity anomalies corresponding to a fluid-solid state transition and a phase IV to phase V transition, respectively. Brillouin scattering spectra has been a powerful tool to investigate the fruitful phases and structure transitions in the hydrogen-rich compound under extreme conditions.