Laser-induced crystallization and phase transitions of As2Se3 under high pressure

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, β-Sb2Te3-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 a-As2Se3 phase.