Ductile inorganic amorphous/crystalline composite Ag4TeS with phonon-glass electron-crystal transport behavior and excellent stability of high thermoelectric performance on plastic deformation

The phonon-glass electron-crystal is an ideal picture for thermoelectric materials. However, amorphous solids such as ceramic and metallic glasses are often excluded from candidate materials for thermoelectrics due to either poor electrical conductivity or trivial Seebeck coefficient. Here, we report the Ag4TeS-based compounds which are amorphous/crystalline composites exhibiting a good promise for thermoelectric application. Their physical transport and mechanical properties can be significantly changed by tuning the Ag content via Ag4±xTeS stoichiometry (x=0, 0.01, 0.02, 0.05, 0.08). This type of amorphous/crystalline composites possess excellent room temperature plastic deformability and exhibit appreciable strain hardening behavior. They can achieve ultralow total thermal conductivity (∼0.26 W m−1 K−1 at room temperature) but display electron transport behavior like a degenerate crystalline semiconductor. The glass-like lattice thermal conductivity of Ag4TeS can be considerably reduced by small nonstoichiometry, and an extremely low value of 0.07 W m−1 K−1 is achieved in Ag4.02TeS at room temperature. As a result, a room temperature zT of 0.58 and a maximum zT of 0.97 at 623 K is achieved, which are the record-high values among the ductile thermoelectric materials reported so far. The Ag4TeS-based amorphous/crystalline composites also have excellent stability of thermoelectric performance on large plastic deformation, demonstrating their potential for thermoelectric applications which require material forming of complex geometry and sophisticated shapes.