Acta Physica Sinica, Volume. 68, Issue 11, 117201-1(2019)
In recent decades, Mg2(Si, Sn) solid solutions have long been considered as one of the most important classes of eco-friendly thermoelectric materials. The thermoelectric performance of Mg2(Si, Sn) solid solutions with outstanding characteristics of low-price, non-toxicity, earth-abundant and low-density has been widely studied. The n-type Mg2(Si, Sn) solid solutions have achieved the dimensionless thermoelectric figure of merit ZT ~1.4 through Bi/Sb doping and convergence of conduction bands. However, the thermoelectric performances for p-type Mg2(Si, Sn) solid solutions are mainly improved by optimizing the carrier concentration. In this work, the thermoelectric properties for p-type Mg2Si0.3Sn0.7 are investigated and compared with those for different p-type dopant Ag or Li. The homogeneous Mg2Si0.3Sn0.7 with Ag or Li doping is synthesized by two-step solid-state reaction method at temperatures of 873 K and 973 K for 24 h, respectively. The transport parameters and the thermoelectric properties are measured at temperatures ranging from room temperature to 773 K for Mg2(1–x)Ag2xSi0.3Sn0.7 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) and Mg2(1–y)Li2ySi0.3Sn0.7 (y = 0, 0.02, 0.04, 0.06, 0.08) samples. The influences of different dopants on solid solubility, microstructure, carrier concentration, electrical properties and thermal transport are also investigated. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images show that the solid solubility for Ag and for Li are x = 0.03 and y = 0.06, respectively. Based on the assumption of single parabolic band model, the value of effective mass ~1.2m0 of p-type Mg2(1–x)Ag2xSi0.3Sn0.7 and Mg2(1–y)Li2ySi0.3Sn0.7 are similar to that reported in the literature. The comparative results demonstrate that the maximum carrier concentration for Ag doping and for Li doping are 4.64×1019 cm–3 for x = 0.01 and 15.1×1019 cm–3 for y = 0.08 at room temperature, respectively; the Li element has higher solid solubility in Mg2(Si, Sn), which leads to higher carrier concentration and power factor PF ~1.62×10–3
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Guo-Cai Yuan, Xi Chen, Yu-Yang Huang, Jun-Xi Mao, Jin-Qiu Yu, Xiao-Bo Lei, Qin-Yong Zhang.
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Received: Feb. 25, 2019
Accepted: --
Published Online: Oct. 30, 2019
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