The ultra-low lattice thermal conductivity dominated by the quartic anharmonicity in Bi-based binary compounds A(3)Bi (A = K, Rb)

In this article, by using self-consistent phonon (SCP) theory, compressed sensing (CS) technology and Boltzmann transport equation (BTE), we studied the role of quartic anharmonicity in the lattice dynamics and thermal transport characteristics of Bi-based binary compounds A(3)Bi (A = K, Rb), with a particular focus on unraveling the impacts of quartic anharmonicity on lattice thermal conductivity kappa(L). By analyzing the phonon dispersion curve and the phonon density of states, we found that the strong quartic anharmonicity, which is mainly caused by the alkali metal atoms A1 in A(3)Bi (A = K, Rb), hardens the vibration frequency of the low-lying phonon branch and ensures the lattice dynamic stability. Through the relaxation time approximation of the Boltzmann transport equation, the calculated kappa(L), considering the three-phonon (3ph) and four-phonon (4ph) scattering process shows an ultra-low value. In addition, we also conducted a detailed analysis of the normalized lattice thermal conductivity, phonon group velocity, phonon scattering rate, and scattering phase space, revealing that the extremely low kappa(L) in A(3)Bi is mainly due to its relatively strong 4ph scattering process. Our research proves the existence of strong quartic anharmonicity in A(3)Bi, and we have studied in detail the influence of 3ph and 4ph scattering processes on the thermal transport properties of A(3)Bi, which has never been reported before. Copyright (C) 2022 EPLA