Utilizing the synchrotron x-ray powder diffraction As2Se3 has been investigated under high pressure in a diamond anvil cell with hydrogen and neon applied as the pressure media. For both systems the amorphous samples were compressed to ca. 2–3 GPa and heated in situ by a laser, which led to their crystallization in the R-3 m, Bi2Te3-type phase. During further compression this phase transforms to the C2/m, βSb2Te3-type structure, and they coexist within the pressure range of 21.5–33.0 GPa. The latter phase is observed up to the highest achieved pressure of 52.0 GPa, revealing no signs of reaction with the hydrogen pressure-transmitting medium. The pressure evolution of the volume of the reported phases has been described by the third-order Birch-Murnaghan equation of state. The relative stability of the experimentally detected crystalline phases is confirmed by the density functional theory calculations. The pressure-driven evolution of the As–Se distances and coordination number has been discussed in comparison to the recent findings concerning the amorphous aAs2Se3 phase.

Tomasz Jaroń, Vitali B. Prakapenka, Viktor V. Struzhkin, “Laser-induced crystallization and phase transitions of As2Se3 under high pressure”, Phys. Rev. B 103, 014103, DOI: abstract

The crystal unit cells and the coordination environments of As in the most important structures of As2Se3 and its heavier siblings considered in this work. As—purple balls; Se—yellow balls.