Solution-Phase Synthesis of Nanostructured AgSbTe₂: Glass-like Thermal Conductivity and High Thermoelectric...

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 AgSbTe₂ 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_0.8Sb_1.2Te_2.2 via a facile hydrothermal route, without any detectable minor secondary phases such as Ag₂Te or Sb₂Te₃, which are commonly present in AgSbTe₂ 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_0.8Sb_1.2Te_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_0.8Sb_1.2Te_2.2, which is almost 100% higher than that of bulk Ag_0.8Sb_1.2Te_2.2. With a high zT maintained across a broad temperature range, the average thermoelectric figure of merit (zT_avg) for nanocrystalline Ag_0.8Sb_1.2Te_2.2 is estimated to be 0.86 from room temperature to 575 K.