Elastic softness of hybrid lead halide perovskites

Afonso da Cunha Ferreira , Antoine Létoublon (1) , Serge Paofai (2) , Makhsud Saidaminov (3) , Stephane Raymond (4) , Claude Ecolivet (5) , Benoit Ruffle (6) , Stéphane Cordier (2) , Claudine Katan (2) , Osman M Bakr (3) , Jacky Even (1) , Philippe Bourges (7)

1 FOTON - Institut des Fonctions Optiques pour les Technologies de l'informatiON
2 ISCR - Institut des Sciences Chimiques de Rennes
3 KAUST - King Abdullah University of Science and Technology [Saudi Arabia]
4 MDN - Magnétisme et Diffusion Neutronique
5 IPR - Institut de Physique de Rennes
6 L2C - Laboratoire Charles Coulomb
7 LLB - UMR 12 - Laboratoire Léon Brillouin

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: MAPbBr_{3}, FAPbBr_{3}, MAPbI_{3}, and α-FAPbI_{3} (MA: methylammonium, FA: formamidinium). We report a complete set of elastic constants characterized 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 α-FAPbI_{3}.

Domaines: Physique [physics]; Chimie

Afonso da Cunha Ferreira, Antoine Létoublon, Serge Paofai, Makhsud Saidaminov, Stephane Raymond, et al.. Elastic softness of hybrid lead halide perovskites. Journées de la Diffusion Neutronique (JDN 2018), May 2018, Roquebrune-sur-Argens, France. ⟨hal-01933567⟩