Enhanced Thermoelectric Properties of Cu 2 SnSe 3 -Based Materials with Ag 2 Se Addition.

In this work, (Ag, In)-co-doped Cu 2 SnSe 3 -based compounds are prepared using a self-propagating high-temperature synthesis process. Ag 2 Se and as-synthesized (Ag, In)-co-doped Cu 2 SnSe 3 -based powders are mixed in a proportion according to the formula of Cu 1.85 Ag 0.15 Sn 0.91 In 0.09 Se 3 / x Ag 2 Se ( x = 0, 3, 4, and 5%), which is followed by a subsequent plasma-activated sintering (PAS) to obtain consolidated composite bulks. A sandwich experiment is designed to reveal the evolution of the microstructure and phase composition of the composite samples during the PAS process. We investigate the reaction mechanism between Ag 2 Se and Cu 2 SnSe 3 -based matrix as well as the influence of Ag 2 Se on the phase composition, microstructure, and thermoelectric transport properties of the composites. Ag 2 Se addition is proven to be effective to improve Ag solubility in the Cu 1.85 Ag 0.15 Sn 0.91 In 0.09 Se 3 matrix and introduce a CuSe secondary phase and an Ag-rich phase at grain boundaries. The electrical conductivity of Cu 1.85 Ag 0.15 Sn 0.91 In 0.09 Se 3 / x Ag 2 Se ( x = 0, 3, 4, and 5%) composites decreases while the Seebeck coefficient increases with increasing Ag 2 Se addition, resulting in an optimized power factor. Moreover, benefiting from the collective phonon scattering at various defects induced by Ag 2 Se addition, the composite samples exhibit significantly suppressed lattice thermal conductivity, which reaches as low as 0.11 W m -1 K -1 at 700 K for the x = 5% sample. A peak figure-of-merit ( ZT ) of 1.26 at 750 K and an average ZT of 0.75 at 300-800 K are obtained for Cu 1.85 Ag 0.15 Sn 0.91 In 0.09 Se 3 /5% Ag 2 Se. This work provides an efficient way to improve average ZT values of Cu 2 SnSe 3 -based compounds for promising power generation at intermediate temperatures.