Two-dimensional overdamped fluctuations of the soft perovskite lattice in CsPbBr3

• Published in: Nature materials 2021-07, Vol.20 (7), p.977-983
• Main Authors: Lanigan-Atkins, T., He, X., Krogstad, M. J., Pajerowski, D. M., Abernathy, D. L., Xu, Guangyong N. M. N., Xu, Zhijun, Chung, D.-Y., Kanatzidis, M. G., Rosenkranz, S., Osborn, R., Delaire, O.
• Format: Article
• Language: English
• Subjects: 639/301/1005/1007; 639/301/119/2795; 639/301/299/946; anharmonic lattice dynamics; Anharmonicity; Biomaterials; Brillouin zones; Chemistry and Materials Science; Condensed Matter Physics; Correlation; Crystals; Damping; electronic devices; First principles; Fluctuations; Halide perovskites; Laboratories; Lattice vibration; Lead compounds; MATERIALS SCIENCE; Metal halides; Nanotechnology; Neutrons; Optical and Electronic Materials; Optical properties; Optimization; Optoelectronics; Perovskites; Phase transitions; phase transitions and critical phenomena; Phonons; photovoltaics; Simulation; solar cells; Thermal properties; Thermodynamic properties; X-ray scattering
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-021-00947-y

Lead halide perovskites exhibit structural instabilities and large atomic fluctuations thought to impact their optical and thermal properties, yet detailed structural and temporal correlations of their atomic motions remain poorly understood. Here, these correlations are resolved in CsPbBr 3 crystals using momentum-resolved neutron and X-ray scattering measurements as a function of temperature, complemented with first-principles simulations. We uncover a striking network of diffuse scattering rods, arising from the liquid-like damping of low-energy Br-dominated phonons, reproduced in our simulations of the anharmonic phonon self-energy. These overdamped modes cover a continuum of wave vectors along the edges of the cubic Brillouin zone, corresponding to two-dimensional sheets of correlated rotations in real space, and could represent precursors to proposed two-dimensional polarons. Further, these motions directly impact the electronic gap edge states, linking soft anharmonic lattice dynamics and optoelectronic properties. These results provide insights into the highly unusual atomic dynamics of halide perovskites, relevant to further optimization of their optical and thermal properties. Neutron and X-ray scattering measurements provide further insight into the anharmonic behaviour of lead halide perovskites, revealing that rotations of PbBr 6 octahedra in CsPbBr 3 crystals occur in a correlated fashion along two-dimensional planes.