First-principles study of the lattice thermal conductivity of the nitride perovskite LaWN3

Recently, LaWN3 nitride perovskite with polar symmetry has been synthesized and has shown a large piezoelectric response. In addition to experimentally measured piezoelectricity and theoretically predicted ferroelectricity, the thermal transport properties of LaWN3 remains unexplored. In this work, the phonon dispersion, lattice thermal conductivity, group velocity, phonon lifetime, phase space, and Grüneisen parameters of LaWN3 are systematically studied using first-principles calculations. The results show that the lattice thermal conductivity of LaWN3 is 3.33 and 3.71 W/(mK) along the a and c axes at 300 K, respectively, which is comparable to some typical ferroelectric oxide perovskites such as PbTiO3 and BaTiO3. Further analyses imply that over 60% of the lattice thermal conductivity of LaWN3 is contributed by the optical phonons. It is found that there exists the coupling effect between the acoustic and low-lying optical phonons which limits the group velocity and the contribution to lattice thermal conductivity of acoustic phonons. Additionally, the four-phonon scattering is found to play an important role in suppressing the lattice thermal conducitivty, which is reduced by ∼50% compared to the values where only three-phonon scattering is considered.