Cu2Se is a p-type semiconducting compound that possesses excellent thermoelectric properties which exhibit great potential for practical applications.

Cu3SbS4-based materials composed of nontoxic, low-cost, and earth-abundant elements potentially exhibit favorable thermoelectric performance. However, some key transport parameters and thermal stability have not been reported. In this work, the effects of Bi and Sn co-doping on thermoelectric properties and the thermal stability of Cu3SbS4 were studied by experiment and theoretical validation. Bi and Sn doping can effectively tune the electrical properties and the electronic band structure. The Bi and Sn doping leads to an increased carrier concentration from 6.4 × 1017 to 7.4 × 1020 cm–3 and a decreased optical band gap from 0.85 to 0.73 eV. The effective mass was increased from ∼3.0 me for Bi-doped samples to ∼4.0 me for Bi and Sn co-doped samples. An enhanced power factor of 1398 μW m–1 K–2 at 623 K was obtained for Cu3Sb1–x–y Bi x Sn y S4 (x = 0.06, y = 0.09). The measurements of elastic properties exhibited a large Grüneisen parameter (γ ∼2) for Cu3SbS4-based materials. Finally, a maximum zT of 0.76 ± 0.02 at 623 K was achieved for Cu3Sb1–x–y Bi x Sn y S4 (x = 0.06, y = 0.05) sample. In addition, Cu3SbS4 materials possess excellent thermal stability after thermal treatment in vacuum at 573 K for totally 500 h and dozens of heating–cooling thermal cycles (300–623–300 K). It indicates that Cu3SbS4 is a robust alternative for Te-free thermoelectric materials at an intermediate temperature range. This work provides feasible guidance to survey the thermal stability of chalcogenides.

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The n-type polycrystalline materials of Ba 8 Ga 16 Ge 30 bulks have been successfully synthesized via the high-temperature and high-pressure (HPHT) method, and their crystal structure has been characterized using the X-ray diffraction. Through the thermoelectric properties measurements and microstructure studies, we know that the improvement of the dimensionless thermoelectric figure-of-merit (ZT) benefits from the low lattice thermal conductivity due to the increased low, medium, and high wavelength phonon scattering by grain boundaries, nanostructures, nanoscale domains, and lattice defects, which are ubiquitous in the synthetic bulk material. As the temperature increases, the power factor (PF) obviously increases, and the thermal conductivity evidently decreases. A minimum thermal conductivity of 0.71 W m −1 K −1 was reached at 773 K for Ba 8 Ga 16 Ge 30 synthesized at 4 GPa. A good ZT value 1.14 was achieved, which was attributed to not only the enhanced PF but also the relative low thermal conductivity.