Effect of the A-Site Cation on the Lattice Thermal Conductivity of Nitride Perovskites

In this report, the effect of A-site cations on the lattice thermal conductivity (κ_L) of nitride perovskites was comparatively studied by first-principles calculations in similar crystal structures, LaWN₃ and YWN₃. The A-site cation is found to induce notable differences in acoustic (0–125 cm^–1) and low-lying optical phonons (125–500 cm^–1), which translate into a large κ_L discrepancy (around 20%). It is worth mentioning that the higher κ_L of LaWN₃ is contributed mostly by atom N in the [WN₆] octahedron, although the average W–N bond length is almost identical for LaWN₃ and YWN₃. Faster group velocity, longer lifetime, and larger Grüneisen parameters in optical branches are observed in LaWN₃, which should be ascribed to the longer distance between the cation La and the [WN₆] octahedron. Our findings provide a deep understanding of the role of the A-site cation in the thermal conductivity of nitride perovskites.