Crystalline Solids with Intrinsically Low Lattice Thermal Conductivity for Thermoelectric Energy Conversion

The extrinsic routes to manipulating phonon transport, for instance, through multiple defects of hierarchical length scales, are proven effective in suppressing the lattice thermal conductivity (κL), but their usefulness primarily relies on the selective scattering of phonons over charge carriers. Alternatively, crystalline solids innately exhibiting a low κL can constitute an attractive paradigm capable of offering the long-sought approach for decoupling electron and phonon transport to realize potential candidates for thermoelectric (TE) energy conversion. In this Perspective, we discuss the correlations between chemical bonding and lattice dynamics in specific materials and the ensuing characteristics underpinning an intrinsically low κL therein, viz., lattice anharmonicity, resonant bonding, intrinsic rattling, part-liquid states, and order–disorder transitions. Knowledge of these aspects should guide the discovery and design of new low-κL solids with potential TE applications.