Preparation And Thermoelectric Properties Of N-type Mg₂(Si/Sn) Based Compounds

On the basis of the main progress of Mg₂Si_1-xSn_x based thermoelectric materials in China and abroad,solid state reaction method was selected in the present paper to synthesis Mg₂Si_1-xSn_x based thermoelectric materials at low temperature followed by SPS rapid densification technology.The influences of solid state reaction and SPS process for the phase structure of the compounds were investigated,and also,the influences of Sn solid solution content,Sb doping amount and SPS process for the thermoelectric properties of Mg₂Si_1-xSn_x compounds were investigated.The following conclusions have been obtained:(1) Using one-step solid state reaction,reacting at 823K for 8～10h,combined with SPS to synthesis Mg₂Si single phase compounds;using one-step solid state reaction,reacting at 873K for 24h,combined with SPS to synthesis Mg₂Sn single phase compounds;using two-step solid state reaction,reacting at 923～973K for 24～80h to gain Mg₂Si_1-xSn_x(0＜x＜1) single phase compounds.With the increase of Sn amount,all spectrum peaks of the compounds gradually shift left,and there are no solid solutions in x=0.2,0.4 and 0.6 content.As Sn content increases,the electrical conductivity increases,the abosolute value of Seebeck coefficient decreases;the lattice thermal conductivity first decreases,and gain the lowest value in x=0.4,then increases with x further increase,reach 1.2～2.1Wm^-1K^-1 at 300～820K;and x=0.2 content gain the highest ZT value,gain ZT_max=0.16 at 640K,enhanced for 23%for the highest value reported now.(2) A series of Mg₂Si_0.6-ySn_0.4Sb_y(0＜y＜0.015) compounds were synthesizes by solid state reaction method,with the using of glove box for mixing and grinding operations,combined with SPS rapid density technology,and we found all compounds are single phase.Carrier concentration in room temperature increase with Sb amount increase,and reach the highest value when y=0.0125,then decrease with y further increase,.The results show that solid solubility of Sb in Mg₂Si_0.6Sn_0.4 compounds is near y=0.0125.As the increase of Sb doping amont,the electrical conductivity first increase and then decrease,the absolute value of Seeeck coefficient first decrease then increase,the thermal conductivity first increase then decrease,the ZT value first increase then decrease,the critical point all is y=0.0125;y=0.0125 compounds gains the highest ZT value,which is 1.11 at 860K,the highest results for Mg₂Si_0.6Sn_0.4 compounds have been reported.SPS process has much influence on the thermoelectric properties for Mg₂Si_1-xSn_x compounds,the thermoelectric properties of Mg₂Si_0.5925Sn_0.4Sb_0.0075 compounds enhanced a lot through the optimization of SPS process.4# samples was gained through slow heating between 773 and 973K,then with a rapid densification course,with 200K/min from 773K to 988K,and gained highest ZT value of 1.16 for 4# sample,enhanced for 16%compared with the sample without SPS optimization.