Elastic Softness of Hybrid Lead Halide Perovskites

Abstract
Much recent attention has been devoted towards unraveling the microscopic optoelectronic properties of hybrid organic-inorganic perovskites. Here we investigate by coherent inelastic neutron scattering spectroscopy and Brillouin light scattering, low frequency acoustic phonons in four different hybrid perovskite single crystals: MAPbBr3, FAPbBr3, MAPbI3, and α-FAPbI3 (MA: methylammonium, FA: formamidinium). We report a complete set of elastic constants characterized by a very soft shear modulus C44. Further, a tendency towards an incipient ferroelastic transition is observed in FAPbBr3. 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 α-FAPbI3.

Citation
Ferreira AC, Létoublon A, Paofai S, Raymond S, Ecolivet C, et al. (2018) Elastic Softness of Hybrid Lead Halide Perovskites. Physical Review Letters 121. Available: http://dx.doi.org/10.1103/PhysRevLett.121.085502.

Acknowledgements
This project has received funding from the European Union’s Horizon 2020 programme, through a FET Open research and innovation action under the Grant agreement No. 687008. M. I. S. acknowledges the support of Banting Postdoctoral Fellowship Program, administered by the Government of Canada.

Publisher
American Physical Society (APS)

Journal
Physical Review Letters

DOI
10.1103/PhysRevLett.121.085502

arXiv
1801.08701

Additional Links
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.085502

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