Ecofriendly Highly Robust Ag8SiSe6-Based Thermoelectric Composites with Excellent Performance Near Room Temperature.

Bi2(TeSe)3 is a dominant n-type thermoelectric material used in commercial applications. However, its toxicity and rarity hamper further large-scale industrial applications. Herein, we develop a Ag8SiSe6-based composite as a promising n-type semiconductor with the advantages of nontoxicity and elemental abundance. Ag8SiSe6 composites with Ag2Se and Si nanoprecipitation are fabricated by a unique precipitation reaction sensitive to the hot pressing process. The energy-filtering effect between these phases optimizes electrical resistivity (∼14.59 μΩ·m) and the Seebeck coefficient (above -150 μV·K-1) of the composites, resulting in a maximum power factor of ∼1772 μW·m-1·K-2(@125 °C), which is the highest value in an argyrodite system near room temperature. Nanoprecipitation of Ag2Se and Si can also scatter more phonons and further reduce the lattice thermal conductivity to 0.20 W·m-1·K-1. As a result, a maximum ZT value of ∼0.9 (@125 °C) and an average ZT value of ∼0.7 (25-200 °C) are obtained in the composite with 12 vol % Ag2Se and 0.23 vol % Si, which is sintered at 525 °C. These thermoelectric properties are comparable to those of a commercial n-type Bi2Te3 compound. In addition, the Ag8SiSe6 composite has robust mechanical properties (Vickers hardness of >110 HV and bending strength of 70.6 MPa), much better than those of other thermoelectric compounds, because of which Ag8SiSe6 has great commercial application as an alternative to Bi2Te3-based compounds.