Solvothermally optimizing Ag₂Te/Ag₂S composites with high thermoelectric performance and plasticity

Silver-based fast ionic conductors show promising potential in thermoelectric applications. Among these, Ag₂S offers unique high plasticity but low electrical conductivity, whereas Ag₂Te exhibits high intrinsic electrical conductivity yet faces limitations due to high thermal conductivity and poor plasticity. Developing a composite thermoelectric material that combines the benefits of both is therefore essential. Here, this study reports the successful synthesis of Ag₂Te/Ag₂S composites via a facile and low-cost solvothermal method. By finely adjusting the composition of Ag₂S and Ag₂Te to obtain the optimized carrier concentration and the enhanced mobility, the figure of merit ZT of Ag₂Te/Ag₂S composites reached ∼0.42 at 373 K and ∼0.38 at 298 K, both surpassing those of pure Ag₂S and Ag₂Te. This increase in ZT also benefits from lattice defects created by the solvothermally synthesized biphasic composition, effectively scattering phonons of various wavelengths and reducing thermal conductivity compared to pure Ag₂Te. Additionally, the plasticity of the Ag₂Te/Ag₂S composites improved considerably over pure Ag₂Te, achieving a bending strain of ∼2.5% (versus ∼1.2% for intrinsic Ag₂Te). This study can fill a critical gap in the research on composite silver-based fast ionic conductors synthesized via wet chemical methods and provide valuable guidance for future exploration.