Effect Of Doping On Thermoelectric Properties Of Ca₉Zn_4.5Sb₉

Due to excessive energy exploitation and serious environmental pollution,the development of thermoelectric technology to improve energy efficiency has become one of the research hot spots.Zintl phase compounds have good thermoelectric properties due to their complex crystal structure and electronic structure,have great potential in the field of thermoelectrics.The higher resistivity of Ca₉Zn_4.5Sb₉ leads to the low thermoelectric figure of merit,so the main purpose of this paper is to reduce the resistivity of the material by doping and adjusting the carrier concentration.Ca₉Zn_4.5-xAg_xSb₉,Ca₉Zn_4.5-xCu_xSb₉ were synthesized by high energy ball milling and hot pressing method to explore the effect of doping Ag and Cu at Zn site on the thermoelectric properties of Ca₉Zn_4.5Sb₉.The results show that doping Ag increases the carrier concentration and carrier mobility of the material,decreases the resistivity,and does not change the Seebeck coefficient.The power factor of Ca₉Zn_4.3Ag_0.2Sb₉ sample at 673 K is about 20%higher than that of undoped one,the thermoelectric figure of merit is about 0.77 at 873 K.After doping with Cu,the carrier concentration,mobility and thermal conductivity of the material are increased,the resistivity and the Seebeck coefficient are lowered,and the thermoelectric figure of the final material is only slightly improved.The effects of doping Li and Yb at Ca site respectively on the thermoelectric properties of Ca₉Zn_4.5Sb₉ were investigated,too.it is found that the Li_0.2Ca_8.8Zn_4.5Sb₉ carrier concentration is the highest,which is twice as high as that of undoped one,and the carrier mobility,resistivity and Seebeck coefficient are both reduced,then the power factor of the sample is reduced.However,the thermal conductivity of Li doped sample is increased,and finally,the thermoelectric figure of the material is not improved.Doping Yb causes the lowering of hole concentration and the increase of its mobility,which ultimately increases the resistivity and Seebeck coefficient of the material.At the same time,Yb doping reduce the thermal conductivity of the material,and the thermoelectric figure of the Yb doped sample is improved.The ZT value of the Yb_0.15Ca_8.85Zn_4.5Sb₉ sample is 0.78 at 773 K.After Sn is substituted for Sb,the carrier concentration of the material increases.The resistivity,Seebeck coefficient and thermal conductivity of the Sn-doped sample increases the power factor and the thermoelectric figure of the final sample do not increase significantly.