Solution-Phase Synthesis of Nanostructured AgSbTe 2 : Glass-like Thermal Conductivity and High Thermoelectric Performance

The realization of ultralow and glass-like lattice thermal conductivity (κ L ) in crystalline solids remains a significant challenge, yet it is pivotal for thermoelectrics. Polycrystalline bulk AgSbTe 2 has long been recognized as a promising mid-temperature thermoelectric material due to its intrinsically low κ L; however, its thermodynamic instability in its pristine form has hindered its practical deployment. Here, we report the simple and scalable synthesis of nanocrystalline, off-stoichiometric, phase-pure Ag 0.8 Sb 1.2 Te 2.2 via a facile hydrothermal route, without any detectable minor secondary phases such as Ag 2 Te or Sb 2 Te 3, which are commonly present in AgSbTe 2 and are known to degrade its intrinsic thermoelectric performance. The solution-phase synthesis and spark plasma sintering promote the formation of cation-ordered nanodomains, yielding nanoscale superstructures (∼5–20 nm) and consequently strain in the lattice, which effectively scatter heat-carrying acoustic phonons. This results in a glass-like κ L with an ultralow value of ∼0.1–0.2 W/m K in the temperature range of 30–575 K. Furthermore, the semiconducting nature of nanocrystalline Ag 0.8 Sb 1.2 Te 2.2 enables an exceptionally high room-temperature Seebeck coefficient of ∼330 μV/K. Cumulatively, these attributes deliver a promising thermoelectric figure of merit ( zT ) of ∼1.2 at ∼575 K in nanocrystalline Ag 0.8 Sb 1.2 Te 2.2, which is almost 100% higher than that of bulk Ag 0.8 Sb 1.2 Te 2.2 . With a high zT maintained across a broad temperature range, the average thermoelectric figure of merit ( zT avg ) for nanocrystalline Ag 0.8 Sb 1.2 Te 2.2 is estimated to be 0.86 from room temperature to 575 K.