High pressure structural and lattice dynamics study of α-In₂Se₃

Layered α-In₂Se₃ has been studied using a combined in situ synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy study in a diamond anvil cell up to 60+ GPa, at room temperature. Helium, which remains fairly hydrostatic up to the highest pressure in this study, was used as the pressure-transmitting medium. The results from both experimental methods reveal a pressure-induced structural phase transition from α-In₂Se₃ to a monoclinic β′-In₂Se₃ structure at ≈1 GPa, in agreement with previous studies. Based on our detailed measurements using both experimental techniques and the F-f formalism, the β′-In₂Se₃ structure remains stable up to 45 GPa, without a clear indication of a phase transition toward the previously reported β-In₂Se₃ phase. Above this pressure, In₂Se₃ adopts a disordered solid-solution-like orthorhombic structure, phase IV. The results are discussed in comparison with the relevant previous studies of α-In₂Se₃ under pressure.