| Though the energy crisis is becoming serious,20%—55%of the energy source still canbe consumed in the form of waste heat.The Thermoelectric materials can transform the heat into electricity.And Thermoelectric(TE)power generation is a promising renewable energy technology for a wide range of applications including flexible electronics,automobiles,and industrial power plants.Thus developing the thermoelectrical materials with high thermoelectric figure of merit(ZT)can be of great significance.Recently,the emerge of SnSe breaks the record of the ZT value(2.4)of the past tenyears,reaching a value of 2.6 along the b direction(923 K,Cmcm phase),such excellent property can be attributed to the reduce of the bandgap and a rather low thermal conductivity.However,the temperature range for the high ZT(800 K-950 K)is small,which is not suitable for application.Meanwhile,the phase change set barrier for crystal growth,therefore we try to obtain the SnSe crystal via tuning the crystal structure,and study its thermal conductivity.In this thesis,the SnSe and PbxSn1-xSe crystal was grown through CVD andBridgman-Stockbarge method,meanwhile their structure,composition as well as the property was characterized thoroughly.The main content including:[1]The XRD and EDS characterization methods illustrated that the maximum X valueof PbxSn1-xSe is 0.23,the doping of the Pb atoms could reduce the transform temperature reduced from 792 K(SnSe)to 722 K(Pbo.23Sno.77Se),the temperature range of the high ZT value could be enlarged.The low temperature thermal conductivity test showed that,increasing the doping amount could reduce the thermal conductivity.[2]From the Raman results,we can know that the rise of the fwhm of the Raman peak and a red shift of the peak position with the Pb atoms doping and the temperature heating up,because the unit cell parameters and disarrangement is increasing.In addition,The first-order temperature coefficients χ could be fitted through the temperature dependence characterization.In which the χ values of the B3g,A2g mode is larger than A3g,this phenomenon is in close relationship with the unique puckered crystal structure of the material,a relatively small value of A3g can be attributed to the weak force between layers,which is also an important reason for the lower thermal conductivity of the a direction.Overall,we successfully tune the phase change temperature and thermal conductivity of the SnSe single crystal via Pb doping,and further studied the tuning mechanism of this kind of material. |
