Atomistic origin of low thermal conductivity in quaternary chalcogenides Cu(Cd, Zn)₂InTe₄

Crystalline semiconductors with intrinsically low lattice thermal conductivity (K) are vital for device applications such as barrier coatings and thermoelectrics. Quaternary chalcogenide semiconductors such as CuCd₂InTe₄and CuZn₂InTe₄are experimentally shown to exhibit lowK, yet its microscopic origin remains poorly understood. Here, we analyse their thermal transport mechanisms using a unified first-principles framework that captures both the Peierls (particle-like propagation,KP) and coherence (wave-like tunnelling,KC) mechanisms of phonon transport. We show that extended antibonding states below the Fermi level lead to enhanced phonon anharmonicity and strong scattering of heat-carrying phonon modes, suppressingKin these chalcogenides. We show thatKPdominates the total thermal conductivity, whileKCremains negligible even under strong anharmonicity of the phonon modes. The heavier Cd ions in CuCd₂InTe₄induce greater acoustic-optical phonon overlap and scattering compared to CuZn₂InTe₄, further lowering thermal conductivity of the former. Additionally, grain boundary scattering in realistic samples contributes to further suppression of thermal transport. Our findings establish the atomistic origins of lowKin quaternary chalcogenides and offer guiding principles for designing low-thermal-conductivity semiconductors.