Ultralow lattice thermal transport and considerable wave-like phonon tunneling in chalcogenide perovskite BaZrS$_3$

TL;DR

This study reveals that BaZrS3 exhibits ultralow lattice thermal conductivity due to phonon softening and anharmonicity, with wave-like phonon tunneling contributing significantly, and demonstrates enhanced thermoelectric performance through material modifications.

Contribution

It provides new insights into phonon transport mechanisms in BaZrS3, highlighting wave-like tunneling and anharmonic effects, and shows how alloying improves thermoelectric efficiency.

Findings

Lattice thermal conductivity of 1.84 W/mK at 300 K.

Wave-like phonon tunneling contributes 18% to thermal transport.

Thermoelectric figure of merit ZT increased from 0.58 to 0.91 at 500 K.

Abstract

Chalcogenide perovskites provide a promising avenue for non-toxic, stable thermoelectric materials. Here, thermal transport and thermoelectric properties of BaZrS$_3$ as a typical orthorhombic perovskite are investigated. An extremely low lattice thermal conductivity $\kappa_L$ of 1.84 W/mK at 300 K is revealed for BaZrS$_3$, due to the softening effect of Ba atoms on the lattice and the strong anharmonicity caused by the twisted structure. We demonstrate that coherence contributions to $\kappa_L$, arising from wave-like phonon tunneling, leading to a 18 \% thermal transport contribution at 300 K. The increasing temperature softens the phonons, thus reducing the group velocity of materials and increasing the scattering phase space. However, it simultaneously reduces the anharmonicity, which is dominant in BaZrS$_3$ and ultimately improves the particle-like thermal transport. Further, by replacing S atom with Se and Ti-alloying strategy, $ZT$ value of BaZrS$_3$ is significantly increased from 0.58 to 0.91 at 500 K, making it an important candidate for thermoelectric applications.