The Thermoelectric Performance Optimization Researches Of Mg/Se Doping On Se-substituted PbTe, GeTe And Their Alloy

PbTe and GeTe are promising thermoelectric materials in the medium temperature, which have potential applications in power generation. It is significant for the energy conservation and emissions reduction, low carbon environmental protection. With the substitution of Se for Te in the PbTe-GeTe alloy, the solubility of Pb in GeTe was increased and the thermoelectric properties were inhanced. In order to further investigate the effects of Mg and Sm elements doping on the phases, microstructures and thermoelectric properties in Se-substitued PbTe, GeTe and PbTe-GeTe alloys, the series of Pb_0.98-xMgxNa₀.02Te₀.5Se₀.5, Ge_1-xMg_xTe₀.7Se₀.3 and Ge₀.75Pb₀.2Sm₀.03Te_1-xSe_x alloys were prepared by melting, quenching, heat treatment and spark plasma sintering （SPS） techniques in this work. The thermoelectric properties of the alloys were optimized.The investigation for the series of Pb_0.98-xMgxNa₀.02Te₀.5Se₀.5 with x= 0,0.02,0.04,0.06, 0.08 and 0.10 shows that the solid solubility of Mg in Pb0.98Na0.02Te0.5Se0.5 alloy was promoted due to the presence of Se. The electrical resistivity and Seebeck coefficient of the alloys increase firstly and then decrease with increasing Mg content and reach the maximum at x= 0.06, while the thermal conductivity decrease first and then increase with increasing Mg content and reach the minimum at x= 0.04. The maximum ZT value of 1.0 was obtained in the sample with Mg content x= 0.04 at 673 K, which was 13.6% higher than 0.88 of the Mg free sample at the same temperature.The investigation for the series of Ge_1-xMg_xTe₀.7Se₀.3 alloys with x= 0.04,0.07,0.10 and 0.12 shows that the small amount of Mg doping in the alloys form MgSe compound mainly, limited were dissolved in the GeTeo.7 Seo.3 solid solution. Mg doping inreases the electrical resistivity, but doesn’t affect the Seebeck coefficient, and the thermal conductivity was reduced significantly. The maximum ZT of 0.6 was obtained in the sample with Mg content x = 0.12 at 673 K, which was 17% higher than 0.51 of the no-doping GeTe alloy at the same temperature.The investigation for the series of Ge₀.75Pb₀.2Sni₀.03Te_1-xSe_x with x= 0,0.1,0.2,0.3,0.4, 0.5 and 0.6 shows that the substitution of Se for Te in the alloy promots the solid solubility of Pb in GeTe-based phase. Sm doping can refine the spinodal decomposition structures. Although the resistivity of the alloy increase with the Se content x, the Seebeck coefficient also increase and the thermal conductivity reduce favorably. As a result, the minimum thermal conductivity of 0.78 W m^-1 K^-1 and the maximum ZT of 1.5 were obtained in the sample with x= 0.5 at 723 K.