Experimental and Theoretical Studies on α-In₂Se₃ at High Pressure

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Indium selenide (In2Se3) exhibits complex phase behavior under pressure.
• Understanding these transitions is crucial for its applications.

Purpose of the Study:

• To investigate the pressure-induced phase transitions of alpha-In2Se3 at room temperature.
• To elucidate the mechanism of the transition from the monoclinic C2/m to the rhombohedral R3-bar m phase.
• To reconcile discrepancies in previous experimental findings.

Main Methods:

• X-ray diffraction and Raman scattering measurements.
• Ab initio total-energy and lattice-dynamics calculations.
• Combined experimental and theoretical approach.

Main Results:

• Confirmed the phase transition sequence: alpha (R3m) -> beta' (C2/m) -> beta (R3-bar m).
• The monoclinic C2/m phase gradually increases symmetry before transforming to R3-bar m above 10-12 GPa.
• Tentatively assigned Raman-active modes for all three phases.
• The second-order nature of the C2/m to R3-bar m transition explains previous measurement discordance.

Conclusions:

• The study clarifies the pressure-induced phase transitions in In2Se3.
• The mechanism of the monoclinic to rhombohedral transition is understood.
• Experimental and computational results resolve existing controversies regarding In2Se3 phases.