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arXiv · 1801.08701

Elastic softness of hybrid lead halide perovskites

A. C. Ferreira·A. Létoublon·S. Paofai·S. Raymond·C. Ecolivet·B. Rufflé·S. Cordier·C. Katan·M. I. Saidaminov·A. A. Zhumekenov·O. M. Bakr·J. Even·Ph. Bourges
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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$_3$.

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A. C. Ferreira, A. Létoublon, S. Paofai, S. Raymond, C. Ecolivet, B. Rufflé, S. Cordier, C. Katan, M. I. Saidaminov, A. A. Zhumekenov, O. M. Bakr, J. Even, Ph. Bourges. 2018-01-26. Elastic softness of hybrid lead halide perovskites. https://doi.org/10.1103/physrevlett.121.085502

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