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

Abstract

Recently, ${\mathrm{LaWN}}_{3}$ 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 ${\mathrm{LaWN}}_{3}$ remains unexplored. In this work, the phonon dispersion, lattice thermal conductivity, group velocity, phonon lifetime, phase space, and Gr\"uneisen parameters of ${\mathrm{LaWN}}_{3}$ are systematically studied using first-principles calculations. The results show that the lattice thermal conductivity of ${\mathrm{LaWN}}_{3}$ 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 ${\mathrm{PbTiO}}_{3}$ and ${\mathrm{BaTiO}}_{3}$. Further analyses imply that over 60% of the lattice thermal conductivity of ${\mathrm{LaWN}}_{3}$ 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 \ensuremath{\sim}50% compared to the values where only three-phonon scattering is considered.