Velocity and Stability of Condensed Polymorphic SiH4: A High-Temperature High-Pressure Brillouin Investigation**Supported by the National Key Research and Development Program (Grant No. 2017YFA0403704), the National Natural Science Foundation of China (Grant Nos. 11474127, 11574112, 11274137, and 11504127), the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT1132), and China Postdoctoral Science Foundation (Grant No. 2015M570265).

Abstract

Silane (SiH4) is a promising hydrogen-rich compound for pursing high temperature superconducting. Previous high pressure measurements of Raman, x-ray diffraction and theoretical studies on SiH4 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 SiH4 by Brillouin scattering measurements at high temperature up to 407 K and high pressure up to 18 GPa. Brillouin scattering frequencies of fluid SiH4 under compression are obtained under isothermal conditions of 300 K, 359 K and 407 K. The SiH4 becomes unstable with increasing temperature and subsequently decomposes into silicon and H2. 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.