Thermoelectric Performances Of Zintl Compound Mg₃Sb₂

Zintl phase Mg₃Sb₂ based thermoelectric material is a kind of typical“electronic crystal-phonon glass”material.Due to its special crystal structure,it is possible to increase the electrical conductivity while reducing the thermal conductivity,and the raw materials are cheap and have no pollution to the environment.Therefore,the Mg₃Sb₂-based compound is a very potential environmentally friendly thermoelectric material.In this thesis,n-type and p-type Mg₃Sb₂ based thermoelectric materials were prepared by high energy ball milling combined with rapid hot-pressing technology,and the effects of doping with Se,Mn,Ag and Zn on the thermoelectric performances were investigated.The results show that Se is an effective n-type dopant.Se doping makes the carrier concentration and Hall mobility increase at the same time,which can effectively reduce the resistivity and significantly increase the power factor.?_L decreases a lot after Se doping,finally,it was found that the sample Mg_3.2Bi_1.4Sb_0.59Se_0.01 with a Se doping amount of x=0.01obtained a high ZT value in the range of 400 K-500 K,between 1.0-1.2,and the calculated PF_eng and ZT_eng were 0.89 W m^-1 K^-1 and 0.85,respectively.Mn doping can effectively suppress the formation of Mg vacancies,leading to an increased Hall mobility and improved power factor at room temperature.The total thermal conductivity was decreased by Mn-doping,mainly comes from the reduction of lattice thermal conductivity.In the end,the room temperature ZT value of the n-type Se/Mn co-doped sample of Mg_3.14Bi_1.4Sb_0.59Se_0.01Mn_0.06 is about 0.8,compared with the undoped sample?0.72?,it increased by about 11.1%.Zn doping increases the carrier concentration and Hall mobility,leading to a significant increase in power factor,especially the power factor at low temperature range.Due to the large mass difference between Zn and Mg,the lattice thermal conductivity significantly reduced by the introduction of point defect scattering during Zn alloying process.Finally,the maximum ZT of the p-type Ag/Zn co-doped sample Mg_2.39Sb₂Ag_0.01Zn_0.6 at 773 K is about0.84,which is about 31%higher than that of the undoped Zn sample.