Entropy engineering induced exceptional thermoelectric and mechanical performances in Cu2-yAgyTe1-2xSxSex

Thermoelectric materials require not only high performance to maximize the energy conversion efficiency but also good mechanical properties to guarantee machinability and reliable operation. It is usually hard to embrace both at once. Herein, we demonstrated the entropy engineering as a promising avenue to realize both exceptional thermoelectric performance and robust mechanical properties in multicomponent alloys Cu2-yAgyTe1-2xSxSex. Entropy engineering by mixing multiple elements stabilizes the high-symmetry hexagonal structure, extends the solubility limit of Ag, and concurrently lessens the phase transition numbers. Furthermore, with co-alloying of S/Se and Ag in Cu2Te, the carrier concentration is largely reduced while the effective mass is enhanced, yielding higher Seebeck coefficient and power factor. Owing to the strong phonon scattering by lattice disorder, the thermal conductivity is decreased by one order of magnitude, reaching 0.29 W m−1 K−1 at room temperature, which is even lower than the amorphous limit. A state-of-the-art peak zT of 1.4 and average zT of 0.74 are achieved in Cu1.9Ag0.1Te0.6S0.2Se0.2. Moreover, the mechanical properties are significantly improved in virtue of the entropy engineering strengthening effect, making it more promising for thermoelectric applications.