The ultra-low lattice thermal conductivity dominated by the quartic anharmonicity in Bi-based binary compounds A3Bi (A = K, Rb)

Abstract 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 . 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 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 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.