Carrier and microstructure tuning for improving the thermoelectric properties of Ag8SnSe6 via introducing SnBr2

The argyrodite compounds (A m/m+ (12− n ) B n + X 2− 6 (A m + = Li + , Cu + , and Ag+; B n + = Ga 3+ , Si 4+ , Ge 4+ , Sn 4+ , P 5+ , and As 5+ ; and X 2− = S 2− , Se 2− , or Te 2− )) have attracted great attention as excellent thermoelectric (TE) materials due to their extremely low lattice thermal conductivity Among them, Ag 8 SnSe 6 -based TE materials have high potential for TE applications. However, the pristine Ag 8 SnSe 6 materials have low carrier concentration (< 10 17 cm −3 ), resulting in low power factors. In this study, a hydrothermal method was used to synthesize Ag 8 SnSe 6 with high purity, and the introduction of SnBr 2 into the pristine Ag 8 SnSe 6 powders has been used to simultaneously increase the power factor and decrease the thermal conductivity ( κ ). On the one hand, a portion of the Br − ions acted as electrons to increase the carrier concentration, increasing the power factor to a value of ∼698 µW·m −1 ·K −2 at 736 K. On the other hand, some of the dislocations and nanoprecipitates (SnBr 2 ) were generated, resulting in a decrease of κ 1 (−0.13 W·m −1 ·K −1 ) at 578 K. As a result, the zT value reaches ∼1.42 at 735 K for the sample Ag 8 Sn 1.03 Se 5.94 Br 0.06 , nearly 30% enhancement in contrast with that of the pristine sample (−1.09). The strategy of synergistic manipulation of carrier concentration and microstructure by introducing halogen compounds could be applied to the argyrodite compounds to improve the TE properties.