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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.

Carbon dioxide exhibits a richness of high pressure polymorphs ranging from typical molecular solids to fully extended covalent solids, which, in turn, makes it a very appealing topic of fundamental research in condensed matter physics and simultaneously provides with valuable insights into the routes of developing possibly novel materials with advanced properties. This marked for the first time that the single crystal X-ray diffraction (XRD) and Brillouin scattering spectroscopy of CO2-I had been performed under high temperature and pressure. Densities, acoustic velocities and elastic moduli of CO2-I were obtained along 300 K, 400 K and 580 K isotherms up to the phase transition boundaries. CO2-I transforms to phase III and phase IV at room temperature (at 12.19 GPa) and 580 K (at 10.83 GPa), respectively. It was observed that high temperature suppresses pressure-induced stress in single crystal CO2-I. All elastic constants and thermal elasticity parameters of CO2-I were obtained and analyzed using finite-strain theory and thermal equation of state modeling. The C11, C12 and KS increase almost linearly with pressure, while shear moduli C44 and G exhibit a downward trend with pressure, showing a noticeable reduction at higher temperature. Elastic anisotropy A is practically independent of pressure along each isotherms and increases from 1.75 to 1.9.

The intriguing vibrational splitting of SiO2 (α‐quartz) is investigated via high‐pressure Raman spectroscopy. The degenerate E(LO + TO) modes, including the 128 and 265 cm−1 vibrations, exhibit a splitting upon compression, and the splitting is found to depend on the initial stress conditions of the sample. The larger the initial stress, the earlier the splitting occurs. When the internal stress is released during compression, the vibrational splitting under pressure is effectively postponed. The study provides a reasonable explanation for the obviously different splitting pressures of E(LO + TO) modes in compressed SiO2 (α‐quartz) in previous reports.