Ultralow lattice thermal conductivity of binary compounds A 2 B (A = Cs, Rb & B = Se, Te) with higher-order anharmonicity correction.

By employing first-principles calculations that integrate self-consistent phonon theory and the Boltzmann transport equation, we have delved into the thermal transport characteristics of hexagonal anisotropic materials A 2 B (A = Cs, Rb and B = Se, Te). Our computational results have disclosed that these A 2 B materials exhibit ultralow lattice thermal conductivity ( κ L ) at room temperature. Specifically, in the case of Cs 2 Te, the κ L values are a mere 0.15 W m -1 K -1 in the a ( b ) direction and 0.22 W m -1 K -1 in the c direction, both markedly less than the thermal conductivity of quartz glass, a conventional thermoelectric material (0.9 W m -1 K -1 ). Importantly, our calculations encompass higher-order anharmonic effects while computing the lattice thermal conductivities of these materials. This is essential since pronounced anharmonicity leads to a decrease in phonon group velocity, and consequently, lowers the κ L values. Our results establish a theoretical foundation for exploring the thermal transport characteristics of anisotropic materials with substantial anharmonicity. Furthermore, the binary compounds A 2 B proffer a gamut of possibilities for a wide range of applications in thermoelectrics and thermal management, owing to their ultralow lattice thermal conductivity.