Predicting the Lattice Thermal Conductivity in Nitride Perovskite LaWN₃ from ab initio Lattice Dynamics

Abstract

Using a density functional theory-based thermal transport model, which includes the effects of temperature (T)-dependent potential energy surface, lattice thermal expansion, force constant renormalization, and higher-order quartic phonon scattering processes, it is found that the recently synthesized nitride perovskite LaWN₃ displays strong anharmonic lattice dynamics manifested into a low lattice thermal conductivity (κ_L ) and a non-standard κ_L ∝T^-0.491 dependence. At high T, the departure from the standard κ_L ∝T^-1 law originates in the dual particle-wave behavior of the heat carrying phonons, which includes vibrations tied to the N atoms. While the room temperature κ_L =2.98 W mK^-1 arises mainly from the conventional particle-like propagation of phonons, there is also a significant atypical wave-like phonon tunneling effect, leading to a 20% glass-like heat transport contribution. The phonon broadening effect lowers the particle-like contribution but increases the glass-like one. Upon T increase, the glass-like contribution increases and dominates above T = 850 K. Overall, the low κ_L with a weak T-dependence points to a new utility for LaWN₃ in energy technology applications, and motivates synthesis and exploration of nitride perovskites.