Disentangling the effects of structure and lone-pair electrons in the lattice dynamics of halide perovskites

• Published in: Nature communications Vol. 15; no. 1; p. 4184
• Main Authors: Caicedo-Dávila, Sebastián, Cohen, Adi, Motti, Silvia G., Isobe, Masahiko, McCall, Kyle M., Grumet, Manuel, Kovalenko, Maksym V., Yaffe, Omer, Herz, Laura M., Fabini, Douglas H., Egger, David A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.05.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/299; 639/638/298; Anharmonicity; Cations; Chemical bonds; Chemistry; Configurations; Dielectric properties; Electrons; Humanities and Social Sciences; Jahn-Teller effect; Laboratories; Lattice design; Molecular dynamics; multidisciplinary; Optoelectronics; Perovskites; Physics; Raman spectra; Science; Science (multidisciplinary); Semiconductors; X-ray diffraction
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-48581-x

Halide perovskites show great optoelectronic performance, but their favorable properties are paired with unusually strong anharmonicity. It was proposed that this combination derives from the n s 2 electron configuration of octahedral cations and associated pseudo-Jahn–Teller effect. We show that such cations are not a prerequisite for the strong anharmonicity and low-energy lattice dynamics encountered in these materials. We combine X-ray diffraction, infrared and Raman spectroscopies, and molecular dynamics to contrast the lattice dynamics of CsSrBr 3 with those of CsPbBr 3 , two compounds that are structurally similar but with the former lacking n s 2 cations with the propensity to form electron lone pairs. We exploit low-frequency diffusive Raman scattering, nominally symmetry-forbidden in the cubic phase, as a fingerprint of anharmonicity and reveal that low-frequency tilting occurs irrespective of octahedral cation electron configuration. This highlights the role of structure in perovskite lattice dynamics, providing design rules for the emerging class of soft perovskite semiconductors. By comparing CsSrBr3 and CsPbBr3 with close structural similarity but the latter lacking lone-pair electrons on the octahedral metal, the authors reveal the similar vibrational anharmonicities in the two perovskites, which disentangles the electronic properties and vibrational anharmonicities.