Elastic softness of hybrid lead halide perovskites

Abstract

Much recent attention has been devoted towards unravelling the microscopic optoelectronic properties of hybrid organic-inorganic perovskites (HOP). Here we investigate by coherent inelastic neutron scattering spectroscopy and Brillouin light scattering, low frequency acoustic phonons in four different hybrid perovskite single crystals: MAPbBr${}_3$, FAPbBr${}_3$, MAPbI${}_3$ and $\alpha$-FAPbI${}_3$ (MA: methylammonium, FA: formamidinium). We report a complete set of elastic constants caracterized by a very soft shear modulus C${}_{44}$. Further, a tendency towards an incipient ferroelastic transition is observed in FAPbBr${}_3$. We observe a systematic lower sound group velocity in the technologically important iodide-based compounds compared to the bromide-based ones. The findings suggest that low thermal conductivity and hot phonon bottleneck phenomena are expected to be enhanced by low elastic stiffness, particularly in the case of the ultrasoft $\alpha$-FAPbI${}_3$.

Supplementary information included

References in corpus (5)

• Necessary and Sufficient Elastic Stability Conditions in Various Crystal Systems
• Mechanical Properties of APbX3 (A=Cs or CH3NH3; X=I or Br) Perovskite Single Crystals
• Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite
• From soft harmonic phonons to fast relaxational dynamics in CH${}_3$NH${}_3$PbBr${}_3$
• Lattice dynamics and the nature of structural transitions in organolead halide perovskites

Cited by in corpus (14)

• Direct evidence of weakly dispersed and strongly anharmonic optical phonons in hybrid perovskites
• Anharmonic electron-phonon coupling in ultrasoft and locally disordered perovskites
• Mechanical Properties of Formamidinium Halide Perovskites FABX3 (FA = CH(NH2)2; B = Pb, Sn; X = Br, I) From First-Principles
• Structure and Binding in Halide Perovskites: Analysis of Static and Dynamic Effects from Dispersion-Corrected Density Functional Theory
• Common acoustic phonon lifetimes in inorganic and hybrid lead halide perovskites
• Decoupled molecular and inorganic framework dynamics in CH${}_3$NH${}_3$PbCl${}_3$
• Ultrafast photoconductivity and terahertz vibrational dynamics in double-helix SnIP nanowires
• Pseudospin-phonon pretransitional dynamics in lead halide hybrid perovskites
• Lifetime-shortened acoustic phonons and static order at the Brillouin zone boundary in the organic-inorganic perovskite CH${}_3$NH${}_3$PbCl${}_3$
• 3D-to-2D Transition of Anion Mobility in CsPbBr${}_3$ under Pressure
• Broadband critical dynamics in disordered lead-based perovskites
• Bond polarizability as a probe of local crystal fields in hybrid lead-halide perovskites
• A perspective on inelastic light scattering spectroscopy for probing transport of collective acoustic excitations
• Mechanical Ductile Detwinning in CH3NH3PbI3 Perovskite