Phonon fingerprints of CsPb₂Br₅

Area of Science:

• Materials Science
• Solid State Physics
• Spectroscopy

Background:

• Cesium lead bromide (CsPb2Br5) is a stable, water-resistant material derived from CsPbBr3 perovskite.
• Coexistence of CsPb2Br5 and CsPbBr3 at the nanoscale can lead to conflicting optical spectroscopy results.
• Understanding the lattice dynamics and phonon behavior of CsPb2Br5 is crucial for its material characterization.

Purpose of the Study:

• To present a comprehensive analysis of polarized Raman spectra for CsPb2Br5 single crystals.
• To determine the symmetry and frequency of Raman-active phonons in CsPb2Br5.
• To investigate the lattice dynamics and stability of CsPb2Br5 using experimental and computational methods.

Main Methods:

• Acquisition of polarized Raman spectra from nonluminescent CsPb2Br5 single crystals.
• Density functional perturbation theory (DFPT) simulations for calculating phonon frequencies and dispersion.
• Comparison of experimental Raman spectra with theoretical predictions.

Main Results:

• Detailed polarized Raman spectra revealed nondegenerate Raman-active phonons accessible from the (001) plane.
• Experimental results showed good agreement with DFPT simulations, validating calculated phonon frequencies.
• Calculated phonon dispersion confirmed the stable lattice dynamics of CsPb2Br5, contrasting with CsPbBr3.

Conclusions:

• CsPb2Br5 exhibits stable lattice dynamics, free from the dynamic disorder observed in CsPbBr3.
• The absence of Cs anharmonic motion coupling to Br atoms contributes to the stability of CsPb2Br5.
• The study provides reliable phonon frequencies for CsPb2Br5, including unobserved modes, aiding future research.