Rare‐Earth Yttrium Doping Advances High‐Performance AgSbTe ₂ Thermoelectrics

Thermoelectric materials require the simultaneous optimization of electronic and thermal transport to achieve high performance. AgSbTe 2 is a promising p‐type thermoelectric material, yet its carrier tuning is limited, and its lattice thermal conductivity remains suboptimal. Here, we introduce Yttrium (Y) doping into AgSbTe 2 as a dual strategy to address these challenges. Optimizing the nominal Y doping composition induces the formation of Y‐rich precipitates that establish coherent interfaces with Ag 2 Te secondary phases, which both enhance phonon scattering and stabilize the microstructure. This approach reduces an ultralow lattice thermal conductivity to 0.26 W m −1 K −1 . Complementary first‐principles calculations reveal that local hybridization broadens the valence band pockets and modifies the density of states, thereby increasing the effective carrier concentration. These synergistic effects yield a peak figure‐of‐merit ZT of ∼2 at 623 K and an average ZT of 1.5 over 323–623 K. Engineering ZT analysis further predicts a conversion efficiency of 14.4 % at a temperature difference of 323 K, highlighting the potential of rare‐earth doping as a pathway for advancing high‐performance thermoelectrics. In addition, experimentally measured single‐leg performance demonstrates a peak conversion efficiency of ∼7.3 % at a temperature difference of 325 K, providing an initial device‐level validation of the Y‐doped AgSbTe 2 system.