Simultaneous Optimization of Thermoelectric Transport and Mechanical Performance in Full‐Zintl CaCd 2 Sb 2 /Mg 3 Sb 2 Thermoelectric Modules

ABSTRACT Achieving both high thermoelectric performance and robust mechanical strength remains a key pursuit for the practical deployment of thermoelectric applications. Herein, a solid‐solution approach is employed in CaCd 2 Sb 2 via alloying with EuMg 2 Sb 2 , achieving a synergistic optimization of electrical and phonon transport and mechanical performance. The incorporation of EuMg 2 Sb 2 facilitates band degeneracy, thereby substantially improving the electrical transport properties. Together with the reduced thermal conductivity, the optimized composition exhibits a peak zT of ∼ 1.4 at 750 K and an average zT of ∼ 0.81 between 300 and 750 K. Furthermore, solid‐solution strengthening markedly enhances the mechanical properties, thereby ensuring mechanical integrity for reliable device integration. Leveraging transient liquid phase bonding, a 2 × 2 full‐Zintl module combining this optimized p‐type material with Mg 3 Sb 2 ‐based n‐type legs achieves a conversion efficiency of ∼ 11% at a temperature difference of 422 K. This work highlights the viability of Zintl phases toward high‐efficiency thermoelectric modules.