Acoustic phonons have long been believed to dominate the lattice thermal conductivity (kappa l) and the contribution of optical phonons can be neglected in crystal structures. KCaBi, as a high-throughput screening semiconductor with ultralow kappa l [J. Am. Chem. Soc. 144, 4448 (2022)], has been demonstrated that the contribution of optical phonons plays an important role in thermal transport. In this work, by solving the Boltzmann transport equation, it is found that the kappa l of KCaBi is 2.2 at 300K, with acoustic phonons dominating the z-direction kappa l and optical phonons contributing ...
