General surfactant-free synthesis of binary silver chalcogenides with tuneable thermoelectric properties

Binary silver chalcogenides (Ag2X, X = S, Se, Te) are a group of intriguing thermoelectric materials. When utilised for thermoelectrics, however, the syntheses of these chalcogenides commonly require energy-intensive, high-temperature melting-annealing processes. Herein, we have developed a general surfactant-free and scalable solution synthesis strategy to nano/micro-particles of binary silver chalcogenides, which requires neither high temperature nor long reaction duration. The chalcogenide particles were spark plasma sintered into pellets with porous structures. By modifying the Ag+/X2− molar ratios in the solution precursors from 2:1 to 2:1.1, the thermoelectric properties of the pellets have been effectively optimised, leading to maximum ZT values of 0.84 at 380 K for Ag2Se, 0.59 at 650 K for Ag2Te and 0.27 at 540 K for Ag2S that are comparable to those of samples fabricated by other synthetic methods, such as melting and annealing. This study provides a general surfactant-free solution approach to binary silver chalcogenide nano/micro-materials with tuneable thermoelectric properties.