Velocity and Stability of Condensed Polymorphic SiH₄: A High-Temperature High-Pressure Brillouin Investigation*

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.

Polymorph selection of magnesium under different pressures: A simulation study

“…The phase that eventually emerges during solidification is not necessarily to be the most stable (lowest energy) phase, but it has to be thermodynamically stable. [44] That is to say, the properties determined by thermodynamic conditions are usually deterministic, while the properties determined by dynamical factors exhibit a certain randomness. Polymorph selection of Mg has been a challenging subject and it is difficult for us to obtain some metastable phases of Mg by only changing the cooling rate.…”

Pressure-induced phase transition in transition metal trifluorides

“…The high pressure thus offers exciting opportunities for discovering new materials that do not exist under ambient conditions. [34][35][36][37][38][39][40] Highpressure does not necessitate the destruction of the MF 6 octahedron in MF 3 systems. In practice, the pressure-induced structural evolution is only the cooperative tilting of the MF 6 octahedra, [41][42][43] which can be summarized as follows: (i) an elongation of the MF 6 octahedra along the c axis leads to a small octahedral strain, (ii) the MF 6 octahedral strain disappears, and (iii) MF 6 octahedral elongation occurs along the a axis.…”

Abnormal Elastic Changes for Cubic-Tetragonal Transition of Single-Crystal SrTiO3

“…Brillouin scattering signal was collected with a 3+3 Tandem Fabry-Pérot Interferometer by employing the symmetric platelet (50 ∘ ) scattering geometries. [29] The excitation source is a single frequency 532 nm laser. The source power is 140 mW and the power on the sample is 40 mW.…”