Elastic softness of hybrid lead halide perovskites

Afonso da Cunha Ferreira (1, 2) , A. Létoublon (1) , Serge Paofai (3) , Stéphane Raymond (4) , C. Ecolivet (5) , Benoit Rufflé (6) , Stéphane Cordier (3) , C. Katan (3) , Makhsud I Saidaminov (7) , Ayan A Zhumekenov (7) , Osman M Bakr (7) , Jacky Even (1) , Philippe Bourges (2)

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

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.

Domaines: Physique [physics]; Chimie

Afonso da Cunha Ferreira, A. Létoublon, Serge Paofai, Stéphane Raymond, C. Ecolivet, et al.. Elastic softness of hybrid lead halide perovskites. Physical Review Letters, 2018, 121 (8), pp.085502. ⟨10.1103/PhysRevLett.121.085502⟩. ⟨hal-01860094⟩