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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]

Diamondlike compound Cu2SnS3 has attracted great attention recently due to its excellent thermoelectric performance and the features of being eco-friendly and low cost. However, the underlying mechanism for its good electrical transports under high carrier concentration range is still not clear. In this work, we synthesized a series of Cu2+xSn1−xS3 (x = 0–0.08) samples. These nonstoichiometric Cu2+xSn1−xS3 samples are polymorph simultaneously crystalizing in the monoclinic, tetragonal, and cubic structures. The characterization on the electrical transports and the analysis on the band structure reveal that the large density-of-states effective mass, high Seebeck coefficient, and high mobility under a high carrier concentration in the Cu2+xSn1−xS3 system are originated from the existence of multiple bands near the edge of the valence band. Likewise, the polymorphic structure has little influence on the electrical transports. A maximum power factor of 12.6 μW cm−1 K−2 at 700 K has been obtained for the nonstoichiometric Cu2.08Sn0.92S3. Combining the low lattice thermal conductivity of these samples, Cu2.08Sn0.92S3 shows a peak dimensionless figure of merit of 0.5 at 700 K. This work is helpful for guiding the future optimization of thermoelectric performance on Cu2SnS3. [ABSTRACT FROM AUTHOR]

As the pseudo-binary alloys between GeTe and Sb2Te3, GeSbTe-based compounds are promising thermoelectric materials. Although Ge2Sb2Te5 and GeSb2Te4 have widely been studied, the thermoelectric properties of GeSb4Te7 have not been well understood yet. In this work, we design a series of GeSb4-xBixTe7 solid solutions and systematically study the variation in the crystal structure, electrical, and thermal transport properties. Alloying Bi effectively reduces the carrier concentration and, thus, enhances the Seebeck coefficient. Meanwhile, the thermal conductivity is greatly reduced via large mass fluctuations. A maximum zT of 0.69 at 550 K and an average zT value of 0.52 between 300 and 700 K have been achieved for GeSb1.5Bi2.5Te7. These findings will promote the understanding and development of GeSbTe-based thermoelectric 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]