Abstract
We examine the lattice thermal conductivities (κl) of Li2X (X=O, S, Se, Te) using a first-principles Peierls-Boltzmann transport methodology. We find low κl values ranging between 12 and 30 W/m-K despite light Li atoms, a large mass difference between constituent atoms and tightly bunched acoustic branches, all features that give ‘high κl’ in other materials including BeSe (630 W/m-K), BeTe (370 W/m-K) and cubic BAs (3150 W/m-K). Together these results suggest a missing “ingredient” in the basic guidelines commonly used to understand and predict κl. Unlike typical simple systems (e.g., Si, GaAs, SiC), the dominant resistance to heat-carrying acoustic phonons in Li2Se and Li2Te comes from interactions of these modes with two optic phonons. These interactions require significant bandwidth and dispersion of the optic branches, both present in Li2X materials. These considerations are important for the discovery and design of new materials for thermal management applications, and give a more comprehensive understanding of thermal transport in crystalline solids.
