Degenerate Lattice-Instability-Driven Amorphization under Compression in Metal Halide Perovskite CsPbI₃

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Halide perovskites are promising for photovoltaics due to excellent optoelectronic properties and low cost.
• External pressure induces reversible phase transitions in halide perovskites, including amorphization.
• Understanding pressure-induced amorphization is crucial for their stability and application.

Purpose of the Study:

• Investigate the origin of pressure-induced amorphization in cesium lead iodide (CsPbI3).
• Determine the critical pressure for the transition from crystalline to amorphous phases.
• Elucidate the underlying mechanisms of lattice instability under pressure.

Main Methods:

• First-principles density functional theory (DFT) calculations.
• Ab initio molecular dynamics (AIMD) simulations.
• Phonon dispersion analysis.

Main Results:

• Amorphous-like structures of CsPbI3 become more stable than the orthorhombic Pbnm phase above 6.66 GPa.
• This calculated transition pressure aligns with experimental observations (4.44 GPa).
• Degenerate lattice instabilities, linked to PbI6 octahedral tilting, emerge at 10 GPa, causing amorphization.

Conclusions:

• Lattice instabilities, specifically degenerate phonon modes related to octahedral tilting, drive amorphization in CsPbI3 under pressure.
• The findings provide fundamental insights into the mechanical behavior of halide perovskites.
• This research contributes to understanding material stability for optoelectronic device applications.