Lattice distortion leads to glassy thermal transport in crystalline Cs$_3$Bi$_2$I$_6$Cl$_3$

TL;DR

This study combines experimental measurements and machine learning simulations to reveal that lattice distortions in crystalline Cs$_3$Bi$_2$I$_6$Cl$_3$ cause glassy thermal transport, providing insights into disorder-induced thermal behavior.

Contribution

It introduces a combined experimental and computational framework to explain glassy thermal transport caused by lattice distortions in crystalline materials.

Findings

Experimental thermal conductivity measurements from 20K to 300K.

Lattice distortions at low temperatures due to atomic size mismatch.

Reproduction of thermal conductivities using lattice-distorted structures and Wigner formulation.

Abstract

The glassy thermal conductivities observed in crystalline inorganic perovskites such as Cs$_3$Bi$_2$I$_6$Cl$_3$ is perplexing and lacking theoretical explanations. Here, we first experimentally measure such its thermal transport behavior from 20~K to 300~K, after synthesizing Cs$_3$Bi$_2$I$_6$Cl$_3$ single crystals. Using path-integral molecular dynamics simulations driven by machine learning potentials, we reveal that Cs$_3$Bi$_2$I$_6$Cl$_3$ has large lattice distortions at low temperatures, which may be related to the large atomic size mismatch. Employing the Wigner formulation of thermal transport, we reproduce the experimental thermal conductivities based on lattice-distorted structures. This study thus provides a framework for predicting and understanding glassy thermal transport in materials with strong lattice disorder.