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Lead-free tin telluride (SnTe) has been viewed as one promising solid thermoelectric material for recovering waste heat in recent years. In this work, SnTe alloys doped with excessive In and Sb have been synthesized by melting, quenching and spark plasma sintering. The Seebeck coefficient has been enhanced by synergistic effect based on resonant levels and increased carrier effective mass especially at low and middle temperature range, and then, the power factor is enlarged. With the reduced electrical and lattice thermal conductivity via co-doping, the total thermal conductivity is decreased. Intrinsic point defect and more grain boundaries lead to reduction in the lattice thermal conductivity through the co-doping. In addition, as the doping level is near the solubility limit, the 200–600 nm, In-rich precipitations have been detected in Sn0.848Sb0.14In0.012Te alloy, which can further reduce the lattice thermal conductivity. Thus, the lowest lattice thermal conductivity of 0.96 W m−1 K−1 is obtained at 800 K. Finally, the maximum figure of merit zT of ~ 0.8 at 800 K has been obtained for Sn0.848Sb0.14In0.012Te alloy, and a relative high average zT of ~ 0.45 in 300–800 K is achieved due to the zT improvement in the low and middle temperature range which indicated that SnTe is a promising candidate for the thermoelectric application.

Thermoelectric properties, phase and microstructural investigation of (Zn1−x−yAlxGay)O, where x = 0.02, y = 0.04, 0.05 and x = 0.03, y = 0.01, 0.02 are studied at a high temperature of 1450 °C in this article. We have focused on the effects of sintering atmospheres on thermoelectric properties, phase, and microstructure in the air as well in the argon atmosphere. The Seebeck coefficient (S) and electrical resistivities (ρ) measured in air and argon atmospheres have an evidential large difference. The air sintered Al, Ga co-doped ZnO has higher power factor (S2σ) of the order 720.9 µW K− 2 m− 1 and lower electrical resistivity (ρ) of 5.803 mΩ cm for the nominal formula (Zn1− x−yAlxGay)O, with x = 0.03, y = 0.01 as compared to the power factor 543.6 µW K− 2 m− 1 and electrical resistivity of the order 1.550 mΩ cm at 692.2 °C sintered in the argon atmosphere at the same temperature i.e. 1450 °C. The power factor of the air sintered sample with x = 0.03, y = 0.01 is 1.4 times higher than the argon sintered sample with the same composition. The difference in power factors and electrical resistivities are linked to sintering atmospheres. We will investigate the effects of sintering atmospheres of the co-doped ZnO and will study thermoelectric properties, phase, and microstructures of the co-doped ZnO.

The limited solid solutions of nominal (1 − x) CuFeO2 − xCuAlO2 have been prepared by conventional solid-state reaction, and thermoelectric property has been measured. From the XRD powder pattern, we found that the major phase of the limited solid solution is rhombohedral delafossite structure when the composition is near the end members. Cubic Cu(Fe,Al)2O4 phase has been formed in composition from x = 0.4 to 0.8. Electrical resistivity of samples with major delafossite structure is lower than that of samples with Cu(Fe,Al)2O4 phase. In the zone of phase transform, the electrical resistivity can be got with lower value, such as x = 0.2, 0.3 and 0.9. The Seebeck coefficient for the limited solid solution with delafossite structure is positive in whole measured temperature range from 300 to 923 K. In the end, the power factor for the limited solid solution with major delafossite structure shows higher value, which is resulted from the lower electrical resistivity by the phase transposition. The highest power factor of 1.14 × 10−4 W/mK2 has been addressed at 907 K for x = 0.2, which value is enhanced by 3–4 times than that of pure phase CuFeO2 or CuAlO2.