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 (kappa 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 kappa L discrepancy (around 20%). It is worth mentioning that the higher kappa 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 Gruneisen 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.