Zintl thermoelectrics: from impactful materials to real-world applications

Thermoelectric technology, capable of directly interconverting heat and electricity, has attracted extensive attention for sustainable energy harvesting and solid-state cooling applications. Among various material families, Zintl materials have emerged as highly competitive candidates as their heterogeneous ionic-covalent bonding provides a favourable basis for phonon-glass electron-crystal transport. Recent advances in chemical design and transport optimization have driven substantial progress at both the material and device levels. To capture these rapid advances, this review provides a comprehensive overview of Zintl thermoelectrics, tracking progress from fundamental crystal chemistry and transport mechanisms to practical engineering. Focusing on Mg₃(Sb,Bi)₂-based compounds together with simple and complex Zintl systems, this review systematically evaluates how bonding and structural characteristics shape intrinsic thermoelectric properties. Key optimization strategies, including carrier engineering, band structure engineering, defect engineering, and microstructure engineering, are discussed with emphasis on the coordinated regulation of electronic and phonon transport. Remaining challenges associated with thermal and chemical stability, mechanical reliability, scalable processing, geometric design, and interface engineering are also critically assessed. Finally, future research priorities are discussed with respect to materials discovery, transport optimization, scalable manufacturing, and device integration.