Mechanisms and design principles for optimizing lattice thermal conductivity in chalcogenides: A comprehensive review

The thermal transport coefficients, especially the lattice thermal conductivity of a material, are crucial in optimizing thermoelectric efficiency and play a significant role in designing future thermoelectric devices. The lattice thermal conductivity (${\kappa }_l$) depends on various factors, including complex lattice configuration and disorder, chemical bonding, anharmonicity, and topological behavior of phonons. Heavy rattling atoms in a unit cell impact heat propagation due to small phonon mean free path, boundary scattering, and anharmonic scattering. In addition, the structural modification through ripples, strain, and local distortions can increase phonon scattering. The disorder and dislocations disrupt phonon propagation, while strain manipulates acoustic phonon scattering. Lone pairs and unusual chemical bonding induce lattice softening and localized phonon vibrations that significantly impede phonon transport. The localization and delocalization of charge carriers through antibonding interactions result in ultralow ${\kappa }_l$ without compromising electron transport properties. The forbidden phonon band gap is another crucial factor that alters the phonon phase space for acoustic-optical interactions, restricting the three-phonon scattering process and emphasizing the vital role of higher-order anharmonic interactions. The emerging concept of the topological behavior (band inversion, Weyl phonon, and nodal lines) of phonons serves as an additional degree of freedom in determining the thermal transport of chalcogenides. Topological phonon points can enhance group velocity through steep linear dispersions or reduce it via flat bands while simultaneously modulating scattering rates due to high phonon density near nodal features. This review integrates experimental and computational insights behind various strategies for chalcogenides, making them future materials for next-generation thermoelectric devices and thermal applications.