Lattice thermal conductivity of ZnO: experimental and theoretical studies

ZnO has been explored using different approaches such as doping, nanostructuring, 2D confinement, and introduction of interface effects for improving thermoelectric performance and lowering thermal conductivity. Herein, the lattice thermal conductivity (κ_L) of ZnO determined from Raman thermometry, the 3ω-method and simulation using three-phonon scattering is presented. The average Debye temperature (θ_D) of A₁(TO) and E₂(high) modes estimated utilizing bond-order-length-strength correlation with local bond averaging effects is ∼422 K. The average κ_L of ZnO calculated using the theoretical coefficient of Slack's equation, θ_D, and Grüneisen parameter (γ) in Slack's equation is 2.75 W m^-1 K^-1, which is significantly lower than the κ_L ∼ 50.9 W m^-1 K^-1 simulated by considering the Perdew-Burke-Ernzerhof functional with Hubbard and non-analytical corrections. The coefficient of Slack's equation is determined from the κ_L ∼ 31 W m^-1 K^-1 of ZnO measured using the 3ω-method for the accurate estimation of the κ_L. The experimental coefficient of Slack's equation with Raman thermometry data yields κ_L ∼ 50.6 W m^-1 K^-1, which is higher than the value obtained using the 3ω-method but consistent with the theoretical value. Thus, three-phonon anharmonicity describes the κ_L of ZnO associated with Raman scattering. The method adopted to calculate κ_L will help for the in-depth analysis of phonon dynamics and the design of wurtzite-ZnO-related power electronics.