Phonon Fingerprints of CsPb2Br5 Single Crystals

TL;DR

This study provides a detailed Raman spectral analysis of CsPb2Br5 single crystals, confirming their lattice stability and phonon characteristics, and compares them with related perovskite materials to understand their structural dynamics.

Contribution

It offers the first comprehensive polarized Raman spectra of CsPb2Br5 and validates density functional perturbation theory predictions for its phonon modes.

Findings

Raman spectra reveal stable lattice dynamics in CsPb2Br5.

Experimental results align with theoretical phonon calculations.

CsPb2Br5 lacks dynamic disorder features present in CsPbBr3.

Abstract

CsPb2Br5 is a stable, water-resistant, material derived from CsPbBr3 perovskite and featuring two-dimensional Pb-Br framework separated by Cs layers. Both compounds can coexist at nano- length scale, which often produces conflicting optical spectroscopy results. We present a complete set of polarized Raman spectra of nonluminescent CsPb2Br5 single crystals that reveals the symmetry and frequency of nondegenerate Raman active phonons accessible from the basal (001) plane. The experimental results are in good agreement with density functional perturbation theory simulations, which suggests that the calculated frequencies of yet unobserved double degenerate Raman and infrared phonons are also reliable. Unlike CsPbBr3, the lattice dynamics of CsPb2Br5 is stable as evidenced by the calculated phonon dispersion. The sharp Raman lines and lack of a dynamic- disorder-induced central peak in the spectra at room temperature indicate that the coupling of Cs anharmonic motion to Br atoms, known to cause the dynamic disorder in CsPbBr3, is absent in CsPb2Br5.