High Frequency Melting Preparation Of ·MgAgSb And Study On The Effect Of Zn And Cd Doping On Its Thermoelectric Properties

MgAgSb is currently reported as a near-room temperature thermoelectric material with the largest thermoelectric value between 400-500 K.However,due to its high content of Mg and Sb,which are volatile,it is difficult to control the composition and performance of the product during smelting.In this paper,MgAgSb bulk materials were successfully prepared by a combination of high-frequency melting and plasma discharge sintering.In order to further improve the thermoelectric figure of merit of MgAgSb,we chose to dope Zn element at the Mg site to reduce its thermal conductivity.On this basis,the choice of doping Cd in the Ag site to increase its carrier concentration,thereby improving the thermoelectric figure of merit.The thermoelectric properties of Mg Zn Ag Sb at different sintering temperatures were also explored.The following main results were obtained:(1)The use of high-frequency smelting to prepare MgAgSb can effectively reduce the volatilization of Mg and Sb,while greatly reducing the preparation time,which is an efficient and convenient preparation method.At the same time,adding excessive Mg can effectively reduce the thermal conductivity of the sample,the lowest value is close to 0.975 W·m^-1·K^-1;on the other hand,adding excessive Sb will not only reduce the thermal conductivity of the sample,while also reducing the resistivity by about 33%.Finally,by adding 3 at.%Mg and 1at.%Sb,a ZT value of about 1.0 can be obtained at 550 K.(2)Based on Mg_1.03Ag Sb_1.01,Mg_1-xZn_xAg Sb(x=1 at.%?2 at.%?3 at.%?4 at.%?5 at.%)series samples were prepared.XRD and EDS analysis showed that a relatively pure single?-MgAgSb phase was obtained.Thermoelectric performance analysis shows that the equivalent doping of Zn does not significantly change the electrical transport properties of the material,but it can not only reduce the lattice thermal conductivity of the sample,but also greatly reduce the electronic thermal conductivity by about 20%.This allows the sample to achieve a maximum ZT value of about 1.26 at 550 K after doping with 2%Zn.(3)Based on Mg_0.8Zn_0.2Ag Sb,Mg_0.98Zn_0.02Ag_1-xCd_xSb(x=0.1 at.%,0.5 at.%,1 at.%,2at.%,3 at.%,4 at.%,5 at.%)series samples were prepared.The results show that due to the doping of the two elements,only a pure?-MgAgSb phase can be obtained when the doping amount is 0.1 at.%and 0.5 at.%.At the same time,although the incorporation of Cd did not reduce the resistivity of the material as expected,to improve the electrical transport performance.However,the incorporation of Cd did not significantly increase the thermal conductivity of Mg_0.8Zn_0.2Ag Sb.Finally,when Cd doped with 1 at.%at 550 K,a ZT value higher than the pure sample of about 1.0 is obtained.This provides a proof that the second doping element of MgAgSb can only be incorporated in trace amounts.(4)The Mg_0.98Zn_0.02Ag Sb samples were sintered at 400?,430?,450?,480?,and500?,respectively.The results show that when the sintering temperature is 450?,the Seebeck coefficient of the sample can be greatly improved,so that the thermoelectric figure of merit of Mg_0.98Zn_0.02Ag Sb is further increased to 1.4 at 550 K.