Exploring the Role of Four-Phonon Scattering in the Lattice Thermal Transport of LaMoN₃

In this work, we systematically investigate the lattice thermal conductivity (κ_L) of LaMoN₃ in the C2/c and R3c phases using first-principles calculations combined with the Boltzmann transport equation. In the C2/c phase, κ_L exhibits strong anisotropy, with values of 0.75 W/mK, 1.89 W/mK, and 0.82 W/mK along the a, b, and c axes, respectively, at 300 K. In contrast, the R3c phase shows nearly isotropic thermal conductivity, with values of 6.28 W/mK, 7.05 W/mK, and 7.31 W/mK along the a, b, and c directions. In both phases, acoustic and low-frequency optical phonons dominate the thermal transport. However, the C2/c phase exhibits increased three-phonon scattering leading to smaller values of κ_L. Additionally, four-phonon scattering plays a dominant role in the C2/c phase, reducing κ_L by approximately 96%, whereas in the R3c phase, it leads to a smaller but still significant reduction of ∼50%. These results highlight the critical role of four-phonon interactions in determining the thermal transport properties of LaMoN₃ and reveal the stark contrast in thermal conductivity between its two structural phases.