Synergistic effects of K-atom rattling, anisotropy, and antibonding states on high thermoelectric performance in KAuSe2

Abstract

This study reveals the synergistic roles of structural rattling, anisotropy, and antibonding states in KAuSe₂ using first-principles calculations and Boltzmann transport theory. The strongly covalent chain [AuSe₂] and weakly bonded K atoms induce rattling vibrations, and together with antibonding states weaken chemical bonding near the band edges, thereby enhancing lattice anharmonicity and phonon scattering, leading to an ultralow lattice thermal conductivity (κ_L) of 0.40 W m⁻¹ K⁻¹ along the a-direction at 700 K. Notably, n-type KAuSe₂ achieves a maximum zT of 1.06 along the c-direction, while p-type KAuSe₂ shows its peak zT of 0.99 along the a-direction, demonstrating strong orientation-dependent thermoelectric optimization. These findings highlight the cooperative control of rattling, anisotropy, and antibonding states for high-performance thermoelectrics.