First-principles study of energy transport in tin oxynitride lattice

Tin dioxide (SnO2) based devices require thermal management for safety and performance. Tin oxynitrides are considered a new class of material that can potentially tune the physicochemical properties of SnO2. Here, we investigate the energy transport in SnO2 polymorphs, Sn3N4, and SnO2-xNx oxynitrides with various compositions (x = 0.34, 0.5, 0.66, 1.00, 1.34, 1.50, and 1.66) utilizing first principles-based phonon calculations. The phonon dispersion curves of the materials extract the phonon energy and group velocity, which determines the energy transport in the lattices. N-rich SnO2-xNx has unique stretching motions of N-2 dimers near 25 THz. The group velocity of SnO2-xNx in the high-frequency region decreases as the nitrogen content (x) in SnO2-xNx increases; the lowered group velocity originates from the slow-moving N atoms. The combined results explain the change in the energy transport as the N concentration increases in SnO2-xNx by comparing the contributions of the small group velocity to those of the phonon energy for distinct vibrational modes.