Achieving High Thermoelectric Properties of Cu2Se via Lattice Softening and Phonon Scattering Mechanism

Co-alloying solid solution was regarded as a convenient approach to optimize the thermoelectric properties. In this study, the densified Cu2–x(MnFeNi)xSe1–yTey (x = 0–0.09; y = 0–0.03) designed by entropy engineering was prepared via microwave melting and hot-pressing sintering. The scattering mechanism and thermoelectric performance of Cu2Se were evaluated. Due to the regulation of the carrier concentration and structural stabilization of the β-phase, the electrical performance was significantly enhanced. Moreover, the infrared spectroscopy analysis and the decrease in sound velocity unambiguously demonstrated the existence of a lattice softening effect of bulk Cu2Se. By manipulating the lattice conductivity using entropy engineering, the thermal transport property gradually decreased (∼0.4 W m–1 K–1 at 300 K) due to the lattice softening effect and phonon scattering mechanism. The obtained zTmax was 1.37 at 750 K in the Cu2.91(MnFeNi)0.09Se0.99Te0.01 sample.