Microstructural transformation for robust and high-efficiency Zintl thermoelectrics

Thermoelectric materials offer an exceptional opportunity to convert waste heat into electricity directly, yet their widespread application remains hindered by intrinsic brittleness and poor processability. Here, we introduce a graded ball milling strategy that fundamentally enhances the mechanical robustness and processability of YbZn₂Sb₂-based thermoelectrics. By refining grain microstructure, increasing dislocation density, and promoting intermediate-angle grain boundaries, this approach enables the fabrication of crack-free, large-size, disc-shaped, and microscale dices while maintaining excellent thermoelectric performance. Extending this strategy to a broader class of brittle Zintl compounds, including AZn₂Sb₂, AMg₂Sb₂, and ACd₂Sb₂ (A = Yb, Mg, Ca, Sr, Ba), we achieve a pre-formation cohesive energy of 9.1 eV atom⁻¹ and relatively low lattice thermal conductivity of 0.5 W m⁻¹ K⁻¹ in Yb_0.5Mg_1.3Zn_1.2Sb₂. Integrated with n-type Mg_3.1Nb_0.1Sb_1.5Bi_0.49Te_0.01, the thermoelectric module achieves a conversion efficiency exceeding 10% under a 458 K temperature gradient, operating for more than 40 hours steadily. This work establishes a scalable and versatile strategy for reconciling mechanical durability with high thermoelectric performance, paving the way for next-generation thermoelectric devices with enhanced reliability and industrial viability.