Intrinsically Low Lattice Thermal Conductivity Derived from Rattler Cations in an AMM′Q₃ Family of Chalcogenides

Crystalline semiconductors exhibiting innate low lattice thermal conductivity (κl) are technologically very important for the development of thermal barrier coatings, thermal data-storage devices, and high-performance thermoelectrics. Here, using first-principles calculations based on density functional theory and anharmonic lattice dynamics, we predict intrinsically low κl (<1 W/m K along the stacking direction for T ≥ 400 K) in many known layered semiconductors, AMM′Q3 (A = Na, K, Cs, Tl; M = Cu; M′ = Zr, Hf; Q = S, Se), that possess chemical bonding heterogeneity. We show that low κl in this class of materials arises from (a) the rattling vibrations of the weakly bonded A atoms, characterized by low-frequency localized phonon branches with very small dispersion that give rise to numerous additional scattering channels and (b) strong lattice anharmonicity which is manifested in the large-mode Gruneisen parameters that increase the phonon scattering rates. Our work uncovers inherent low κl in this previously unexplored class of metal chalcogenides which should open up opportunities for applications of these compounds in various thermal energy management devices.