In:
Acta Physica Sinica, Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences, Vol. 68, No. 11 ( 2019), p. 117201-
Abstract:
In recent decades, Mg〈sub〉2〈/sub〉(Si, Sn) solid solutions have long been considered as one of the most important classes of eco-friendly thermoelectric materials. The thermoelectric performance of Mg〈sub〉2〈/sub〉(Si, Sn) solid solutions with outstanding characteristics of low-price, non-toxicity, earth-abundant and low-density has been widely studied. The n-type Mg〈sub〉2〈/sub〉(Si, Sn) solid solutions have achieved the dimensionless thermoelectric figure of merit 〈i〉ZT〈/i〉 ~1.4 through Bi/Sb doping and convergence of conduction bands. However, the thermoelectric performances for p-type Mg〈sub〉2〈/sub〉(Si, Sn) solid solutions are mainly improved by optimizing the carrier concentration. In this work, the thermoelectric properties for p-type Mg〈sub〉2〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 are investigated and compared with those for different p-type dopant Ag or Li. The homogeneous Mg〈sub〉2〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 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 Mg〈sub〉2(1–〈i〉x〈/i〉)〈/sub〉Ag〈sub〉2〈i〉x〈/i〉〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 (〈i〉x〈/i〉 = 0, 0.01, 0.02, 0.03, 0.04, 0.05) and Mg〈sub〉2(1–〈i〉y〈/i〉)〈/sub〉Li〈sub〉2〈i〉y〈/i〉〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 (〈i〉y〈/i〉 = 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 〈i〉x〈/i〉 = 0.03 and 〈i〉y〈/i〉 = 0.06, respectively. Based on the assumption of single parabolic band model, the value of effective mass ~1.2〈i〉m〈/i〉〈sub〉0〈/sub〉 of p-type Mg〈sub〉2(1–〈i〉x〈/i〉)〈/sub〉Ag〈sub〉2〈i〉x〈/i〉〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 and Mg〈sub〉2(1–〈i〉y〈/i〉)〈/sub〉Li〈sub〉2〈i〉y〈/i〉〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 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 4.64×10〈sup〉19〈/sup〉 cm〈sup〉–3〈/sup〉 for 〈i〉x〈/i〉 = 0.01 and 15.1×10〈sup〉19〈/sup〉 cm〈sup〉–3〈/sup〉 for 〈i〉y〈/i〉 = 0.08 at room temperature, respectively; the Li element has higher solid solubility in Mg〈sub〉2〈/sub〉(Si, Sn), which leads to higher carrier concentration and power factor 〈i〉PF〈/i〉 ~1.62×10〈sup〉–3〈/sup〉 〈inline-formula〉〈tex-math id="Z-20190527102739-2"〉\begin{document}${\rm W}\cdot{\rm m^{–1}}\cdot{\rm K^{–2}}$\end{document}〈/tex-math〉〈alternatives〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20190247_Z-20190527102739-2.jpg"/〉〈graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="11-20190247_Z-20190527102739-2.png"/〉〈/alternatives〉〈/inline-formula〉 in Li doped samples; the higher carrier concentration of Li doped samples effectively suppresses the bipolar effect; the maximum of 〈i〉ZT〈/i〉 ~0.54 for Mg〈sub〉1.92〈/sub〉Li〈sub〉0.08〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 is 58% higher than that of Mg〈sub〉1.9〈/sub〉Ag〈sub〉0.1〈/sub〉Si〈sub〉0.3〈/sub〉Sn〈sub〉0.7〈/sub〉 samples. The lattice thermal conductivity of Li or Ag doped sample decreases obviously due to the stronger mass and strain field fluctuations in phonon transport.
Type of Medium:
Online Resource
ISSN:
1000-3290
,
1000-3290
DOI:
10.7498/aps.68.20190247
Language:
Unknown
Publisher:
Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences
Publication Date:
2019
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