Anharmonicity and ultralow thermal conductivity in layered oxychalcogenides BiAgOCh (Ch = S, Se, and Te)

Abstract

Understanding the lattice dynamics and low thermal conductivities of oxychalcogenide materials is critical to the development of a new generation of better thermoelectric oxide materials. Here we systematically investigate the lattice vibrational modes as well as phonon thermal conductivity of experimentally synthesized layered oxychalcogenides BiAgOCh (Ch = S, Se, and Te). First-principles calculations indicate that BiAgOSe and BiAgOTe are dynamically stable and low-thermal-conductivity materials. The room-temperature lattice thermal conductivity for BiAgOTe is calculated to be 0.53 W m⁻¹ K⁻¹, which is smaller than that (0.88 W m⁻¹ K⁻¹) of the promising thermoelectric material BiCuOSe. The strong anharmonicity in BiAgOTe causes short lifetime and low group velocity, which accordingly gives rise to ultralow thermal conductivity in BiAgOTe compounds. Our work of the insights into the lattice dynamics and low thermal conductivity will help the development of high-performance thermoelectric oxide materials.