Phonon lifetimes and mode softening in cubic Cs2AgBiBr6

Published

June 2, 2025

Author(s)

Zihan Zhang, Peter Gehring, Adam H. Slavney, Julian A. Vigil, Tao Hong, Jose Rodriguez Rivera, Johan Klarbring, Hemamala Karunadasa, Michael Toney, Nicholas Weadock

Abstract

Metal halide perovskites (MHPs) have emerged as noteworthy candidates for photovoltaic applications in recent years. Their high power-conversion efficiency is largely attributed to the structure-function relationship, which is not well understood. In this study, we examine the low-frequency phonons of the double perovskite Cs2AgBiBr6 using neutron inelastic scattering. We find that the acoustic phonon lifetimes decrease from 16 to 3 ps along Γ to X, which is indicative of significant anharmonicity that contributes to the ultralow thermal conductivity. Additionally, we observe a linear temperature dependence of the square of the zone-center soft optical phonon energy, which is consistent with a weakly first-order displacive cubic-tetragonal structural phase transition. These results provide a deeper understanding of the lattice dynamics and phase transitions in MHPs as well as the effects of anharmonicity by comparison with prototypical hybrid organic-inorganic MHPs, (CH3NH3) PbX3 (X = Br, I).

Citation

Newton

Volume

1

Issue

4

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.newton.2025.100097

Local Download

Keywords

lattice dynamics, soft modes, perovskite, halides, photovoltaic, neutron scattering

Citation

Zhang, Z. , Gehring, P. , Slavney, A. , Vigil, J. , Hong, T. , Rodriguez Rivera, J. , Klarbring, J. , Karunadasa, H. , Toney, M. and Weadock, N. (2025), Phonon lifetimes and mode softening in cubic Cs2AgBiBr6, Newton, [online], https://doi.org/10.1016/j.newton.2025.100097, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959507 (Accessed October 1, 2025)