Boosting Thermoelectric Properties of High-Entropy Chalcogenides through Local Structural Distortion and Tailored Chemical Bonding

Controlling the local structure of high-entropy materials offers a promising pathway to resolve the trade-off of electron and phonon transport behaviors, which unlocks their full potential in thermoelectric applications. Herein, utilizing time-of-flight neutron total scattering and advanced multiscale simulations, we unveil the intricate local structures spanning both short- and long-range scales in high-entropy chalcogenides AgMnPbSbTe₄ and AgMnGePbSbTe₅, characterized by pronounced long-range cation disordering and well-defined short-range ordering. Notably, pair distribution function refinements revealed substantial discrepancies near 3 Å, unequivocally indicating significant local distortions from PbTe. Besides enhancing Pb-site asymmetry, the high-entropy strategy also triggers chemical bonding evolutions from purely ionic interactions in PbTe to mixed covalent-ionic features in AgMnPbSbTe₄, and ultimately to more robust covalent-ionic interactions in AgMnGePbSbTe₅. This transformation produces a 3-fold enhancement in electrical conductivity for AgMnGePbSbTe₅ relative to AgMnPbSbTe₄, and an orders-of-magnitude improvement over PbTe. Due to the enhanced covalent character imparted by Ge-Te bonding and weakened local octahedral structural distortions with long-ranged scales, the lattice thermal conductivity of AgMnGePbSbTe₅ surpasses that of AgMnPbSbTe₄ across the entire temperature range. By optimizing high-entropy materials from the local chemical order, we achieve a maximum ZT of 1.66 at 750 K in pure AgMnGePbSbTe₅, significantly outperforming intrinsic PbTe (∼ 0.26 at 720 K) and other PbTe-based composites. Our findings not only elucidate the underlying mechanisms governing the anomalously low thermal conductivity in high-entropy materials but also establish a correlation between local structural distortions and thermoelectric performance, thereby providing critical insights for the rational design of next-generation thermoelectric materials.