Solvothermal preparation of silver selenide doped by sulfur and its thermoelectric properties

Silver selenide (Ag₂Se) is a typical thermoelectric material suitable for application near room temperature. Doping heteroatom is an effective method to optimize the thermoelectric properties. However, the precise doping of Ag₂Se prepared by the wet chemical methods is difficult to accomplish. To achieve precise control of doping content, which is important to obtain Ag₂Se-based materials with high thermoelectric performance, the Ag₂Se powders were synthesized by a hydrothermal method using ethylenediamine as the solvent, silver nitrate (AgNO₃) and elemental selenium (Se) as the raw materials. Then, the matrix Ag₂Se was doped with elemental sulfur(S) by a melting method, and bulk materials with high thermoelectric performance is prepared by a spark plasma sintering (SPS). X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) were used to conduct phase analysis and microscopic element analysis of the sample doped with sulfur in different content, and the thermoelectric performance at 300-400 K was tested by a thermoelectric performance test system. The result shows that the doped sample achieves a significant increase in Seebeck coefficient(α) and a decrease in thermal conductivity(κ) in the low temperature phase. The Seebeck coefficient (α) of the sample with a doping content of 3% mole is about -152 μV·K^{- 1} at 393 K, and the thermal conductivity (κ) is 0.91 W·m^-1·K^-1 at 393 K. Finally, the sample doped by 3% molar sulfur reaches a peak zT to 0.81 at 393 K.