Ultralow Lattice Thermal Transport and Considerable Wave-like Phonon Tunneling in Chalcogenide Perovskite BaZrS₃

Chalcogenide perovskites provide a promising avenue for nontoxic, stable thermoelectric materials. Here, the thermal transport and thermoelectric properties of BaZrS₃ as a typical orthorhombic perovskite are investigated. An extremely low lattice thermal conductivity κ_L of 1.84 W/mK at 300 K is revealed for BaZrS₃, 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 κ_L, arising from wave-like phonon tunneling, lead to an 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 BaZrS₃ and ultimately improves the particle-like thermal transport. In addition, via replacement of the S atom with Se- and Ti-alloying strategy, the ZT value of BaZrS₃ is significantly increased from 0.58 to 0.91 at 500 K, making it an important candidate for thermoelectric applications.