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Doping And Thermoelectric Properties Of YbZn2Sb2 Based Zintl Phase Thermoelectric Materials

Posted on:2011-12-29Degree:MasterType:Thesis
Country:ChinaCandidate:Z LiangFull Text:PDF
GTID:2121360305981916Subject:Materials science
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Zintl compound YbZn2Sb2 with trigonal crystal system is a promising thermoelectric material. Recently, many researches of YbZn2Sb2 based Zintl phase focused on the effect of element doping at Yb and Zn sites on the thermoelectric properties. In this thesis, a non-equilibrium new method of the combination of melting, quenching and spark plasma sintering was developed to prepare rapidly YbZn2Sb2 based porous thermoelectric materials. The preparation period of the novel method was remarkably shortened from 22 days by traditional method to less than 17 hours by the new method. The nanoporous YbZn2Sb2 based thermoelectric materials, with nominal composition of YbInxZn2-xSb2 (0≤x≤0.8), YbIn0.1Zn1.9Sb2-xGex (0≤x≤0.25) and YbZn2Sb2-xGex(0≤x≤0.15), were successfully synthesized by this method, which have In doping of Zn site, Ge doping of Sb site, and In and Ge double doping, respectively. It was found that all YbZn2Sb2 based thermoelectric materials composed of main YbZn2Sb2 and trace Yb9Zn4.5Sb9, having layer microstructure and an abundance of nanopores with 20~100 nm in size.For the p-type YbZn2Sb2 based porous thermoelectric materials YbInxZn2-xSb2 (x=0,0.02 0.04,0.05,0.06,0.08,0.1,0.12,0.16,0.2,0.4,0.6,0.8), In substitution for Zn caused the linear increase in lattice parameters a and c with increasing x. The solid-solution limit of In impurity at Zn site is about 0.1. The thermoelectric properties of YbInxZn2-xSb2 in 300~875 K indicated that the electrical conductivity and the thermal conductivity decreased, and Seebeck coefficient increased with increasing the x in the range of x≤0.08. However, the electrical conductivity and thermal conductivity increased, Seebeck coefficient decreased with increasing the x when x≥0.1. The thermoelectric properties of YbInxZn2-xSb2 porous thermoelectric materials are better than these of YbInxZn2-xSb2 compact bulk materials with the same chemical composition prepared by traditional technique. ZT values of YbZn2Sb2 nanoporous material reached to 0.27 at 500 K and 0.58 at 875 K, increased by 69% and 12% compared with these of YbZn2Sb2 compact bulk material, respectively. The highest ZT value of YbIn0.1Zn1.9Sb2 nanoporous material reaches 0.65 at 873 K, showing 23% higher than the ZT of 0.53 of YbIn0.1Zn1.9Sb2 compact bulk material.The thermoelectric properties of Ge doped YbZn2Sb2-xGex (x=0,0.05,0.08,0.1, 0.15) and (In, Ge) co-doped YbIn0.1Zn1.9Sb2-xGex(x=0,0.005,0.01,0.03,0.10,0.15, 0.20,0.25) p-type YbZn2Sb2 based porous materials in 300~875 K were measured. The results showed that the electrical conductivity and thermal conductivity increased, Seebeck coefficient decreased, and ZT values decreased with increasing the x (except for YbZn2Sb1.95Ge0.05). Compared with the thermoelectric properties of YbZn2Sb2 porous material in 300~875 K, the electrical conductivity of YbZn2Sb1.95Ge0.05 porous material almost unchanged while Seebeck coefficient remarkably increased, as a result, the highest ZT value reaches 0.68 at 875 K, increased by 26%. These results indicate that trace Ge doping at Sb site could significantly enhance the thermoelectric properties of YbZn2Sb2 compound.
Keywords/Search Tags:Zintl phase thermoelectric material, non-equilibrium rapid technique, nanoporous structure, thermoelectric property
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