Aliovalent Dilute Doping and Nano‐Moiré Fringe Advance the Structural Stability and Thermoelectric Performance in β‐Zn4Sb3

Abstract Thermoelectric (TE) generators have come a long way since the first commercial apparatus launched in the 1950s. Since then, the β ‐Zn 4 Sb 3 has manifested its potential as a cost‐effective and environmentally friendly TE generator compared with the tellurium‐bearing TE materials. Although the β ‐Zn 4 Sb 3 features an intrinsically low thermal conductivity κ , it suffers from a long‐lasting structural instability issue arising from the highly mobile zinc ions. Herein, the dilute Ga dopant gives rise to the aliovalent substitution, lowers the mobile zinc ions, and optimizes the hole carrier concentration n H simultaneously. Meanwhile, the formation of nano‐moiré fringes suggests the modulated distribution of point defect that results from soluble Ga in a β ‐Zn 4 Sb 3 lattice, which elicits an ultralow lattice thermal conductivity κ L = 0.2 W m −1 K −1 in a (Zn 0.992 Ga 0.008 ) 4 Sb 3 alloy. Hence, a fully dense β ‐Zn 4 Sb 3 incorporated with the dilute Ga doping reveals superior structural stability with a peak zT > 1.4 at 623 K. In this work, the aliovalent dilute doping coupled with phase diagram engineering optimizes the fluxes of moving electrons and charged ions, which stabilizes the single‐phase β ‐Zn 4 Sb 3 while boosting the TE performance at the mid‐temperature region. The synergistic strategies endow the ionic crystals with a thermodynamic route, which opens up a new category for high‐performance and thermal robust TE alloys.