Enhanced plasticity in Ag-excessive Ag2Se-based thermoelectric materials

Recently, Ag 2 Se has attracted great interest due to its excellent room-temperature thermoelectric (TE) performance, interesting mechanical properties, and environmental friendliness. Tuning the Ag stoichiometry is a conventional strategy to optimize the TE performance of Ag 2 Se-based materials, but the effects of Ag content on the mechanical properties are still unclear. In this work, we find Ag-excess has weak influence on the plasticity of Ag 2 Se, but can significantly enhance the plasticity of S-alloyed Ag 2 Se. The Ag-excessive Ag 2.01 Se 0.7 S 0.3 can endure large bending strain above 20% without cracking, comparable with those of many metals. The improved plasticity is possibly caused by the increased density of Ag–S bonds. The TE figure-of-merit of plastic Ag 2.01 Se 0.7 S 0.3 reaches 0.53 at room temperature. The flexible TE device consisting of free-standing Ag 2.01 Se 0.7 S 0.3 films shows high maximum material normalized power density up to 0.20 W/m under the temperature difference of 25 K. This work sheds light on the further investigation of mechanical properties of Ag-based TE materials. • Ag-excess can significantly enhance the plasticity and modify the elastic moduli of Ag 2.01 Se 0.7 S 0.3 . • Ag-excessive Ag 2.01 Se 0.7 S 0.3 can endure large bending (>20%) and compressive (>50%) strains without cracking. • Improved plasticity in Ag-excessive Ag 2.01 Se 0.7 S 0.3 is possibly caused by the increased density of Ag–S bonds. • PF and zT of Ag 2.01 Se 0.7 S 0.3 at room temperature are 21.8 μW·cm –1 ·K –2 and 0.53, respectively.