Common acoustic phonon lifetimes in inorganic and hybrid lead halide perovskites

Abstract

The acoustic phonons in the organic-inorganic lead halide perovskites have been reported to have anomalously short lifetimes over a large part of the Brillouin zone. The resulting shortened mean free paths of the phonons have been implicated as the origin of the low thermal conductivity. We apply neutron spectroscopy to show that the same acoustic phonon energy linewidth broadening (corresponding to shortened lifetimes) occurs in the fully inorganic CsPbBr${}_3$ by comparing the results on the organic-inorganic CH${}_3$NH${}_3$PbCl${}_3$. We investigate the critical dynamics near the three zone boundaries of the cubic $Pm\overline{3}m$ Brillouin zone of CsPbBr${}_3$ and find energy and momentum broadened dynamics at momentum points where the Cs-site ($A$-site) motions contribute to the cross section. Neutron diffraction is used to confirm that both the Cs and Br sites have unusually large thermal displacements with an anisotropy that mirrors the low temperature structural distortions. The presence of an organic molecule is not necessary to disrupt the low-energy acoustic phonons at momentum transfers located away from the zone center in the lead halide perovskites and such damping may be driven by the large displacements or possibly disorder on the $A$ site.

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• The Disorder Origin of Raman Scattering In Perovskites Single Crystals
• Decoupled molecular and inorganic framework dynamics in CH${}_3$NH${}_3$PbCl${}_3$
• On the question of dynamic domains and critical scattering in cubic methylammonium lead triiodide
• Untangling the Raman spectrum of cubic and tetragonal BaZrO${}_3$
• Lattice dynamics and spin excitations in the metal-organic framework [CH${}_3$NH${}_3$][Co(HCOO)${}_3$]
• Bond polarizability as a probe of local crystal fields in hybrid lead-halide perovskites
• Broadband critical dynamics in disordered lead-based perovskites
• Neutron scattering studies of complex lattice dynamics in energy materials