Mechanism of the low thermal conductivity in novel two-dimensional NaCuSe

Low lattice thermal conductivity is crucial to obtain an excellent thermoelectric figure of merit (ZT) in thermoelectric (TE) materials. Herein, we study the phonon transport properties of two-dimensional (2D) NaCuSe using first-principles calculations. NaCuSe has an intrinsically low lattice thermal conductivity, 2.46 W/mK at 300 K, which originates from its low mean sound velocity (vm) and strong phonon anharmonicity. By utilizing the crystal orbital Hamilton population (COHP) analysis, we attribute low vm to the filling of anti-bonding orbitals between Cu-3d and Se-4p states, giving rise to the weak chemical bonds. Also, this research investigates the scattering processes (the out-of-plan acoustic mode (ZA) + optical mode(O) -> O(ZA + O -> O), the in-plane transverse acoustic mode (TA) + O -> O(TA + O -> O), and the in-plane longitudinal acoustic mode (LA) + O -> O(LA + O -> O). The results demonstrate that NaCuSe is of strong phonon anharmonicity, which could guide to discover and design of new TE materials.

Automated summary

In this study, the phonon transport properties of two-dimensional NaCuSe were investigated using first-principles calculations. It was found that NaCuSe exhibits low lattice thermal conductivity due to its low mean sound velocity and strong phonon anharmonicity. The weak chemical bonds caused by the filling of anti-bonding orbitals between Cu and Se atoms contribute to the low mean sound velocity. Additionally, the scattering processes were investigated, and it was revealed that NaCuSe has strong phonon anharmonicity, which could guide the discovery and design of new thermoelectric materials.