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Ge-Sb-Te compounds (GST), the well-known phase-change materials, are considered to be promising thermoelectric (TE) materials due to their decent thermoelectric performance. While Ge2Sb2Te5 and GeSb2Te4 have been extensively studied, the TE performance of GeSb4Te7 has not been well explored. Reducing the excessive carrier concentration is crucial to improving TE performance for GeSb4Te7. In this work, we synthesize a series of Se-alloyed GeSb4Te7 compounds and systematically investigate their structures and transport properties. Raman analysis reveals that Se alloying introduces a new vibrational mode of GeSe2, enhancing the interatomic interaction forces within the layers and leading to the reduction of carrier concentration. Additionally, Se alloying also increases the effective mass and thus improves the Seebeck coefficient of GeSb4Te7. The decrease in carrier concentration reduces the carrier thermal conductivity, depressing the total thermal conductivity. Finally, a maximum zT value of 0.77 and an average zT value of 0.48 (300–750 K) have been obtained in GeSb4Te5.5Se1.5. This work investigates the Raman vibration modes and the TE performance in Se-alloyed GeSb4Te7 sheddinglight on the performance optimization of other GST materials. [ABSTRACT FROM AUTHOR]

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 Cu 2- y Ag y Te 1-2 x S x Se x. 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 Cu 2 Te, 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 Cu 1.9 Ag 0.1 Te 0.6 S 0.2 Se 0.2. Moreover, the mechanical properties are significantly improved in virtue of the entropy engineering strengthening effect, making it more promising for thermoelectric applications. Record-high average zT of 0.74 and remarkably improved compressive strength were achieved in multicomponent alloys Cu 2- y Ag y Te 1-2 x S x Se x through entropy engineering [Display omitted]. [ABSTRACT FROM AUTHOR]