Preparation And Performance Optimization Of Tin Selenide-based Thermoelectric Materials

The directly conversion between thermal energy and electric energy can be realized in thermoelectric materials,and the conversion efficiency can be determined by dimensionless thermoelectric figure of merit ZT=S²σ/κand temperature ratio at both ends of heat and cold.SnSe-based thermoelectric materials have the highest ZT in medium-high temperature,however,the performance of tin selenide thermoelectric materials without effective doping is not ideal.The tin selenide thermoelectric materials have low thermal conductivity,but the ZT value is not high because of its low carrier concentration and poor electrical transmission performance.To enhance the conversion efficiency of SnSe-based thermoelectric materials,the main way is to optimize the power factor of SnSe-based materials without increasing the thermal conductivity.To optimize its power factor,the optimization of electrical conductivity and Seebeck coefficient is necessary.The method of preparing the materials include to prepare the powder by mechanical alloying（MA）and then to prepare the tin selenide block by the spark plasma sintering（SPS）.It is convenient for us to introduce impurities or vacancies in SnSe-based thermoelectric materials by this preparation method.Moreover,the crystalline grain of tin selenide are homogeneous and the materials are compact by this preparation method.In this work,we try to introduce vacancies to improve the conductivity of the materials,and optimize the Seebeck coefficient of materials,to improve the thermoelectric figure of merit.We have prepared n type tin selenide semiconductor materials such as SnSe_0.8,SnSe_0.9.9 and SnSe_0.95,and P type semiconductor materials such as SnSe_1.03,SnSe_1.05 and SnSe_1.1 by introducing vacancies.In this work,both P type and N type semiconductors were prepared with only two elements Sn and Se,and the highest ZT values obtained in SnSe_1.05 sample（ZT is about 0.65 at 773 K）,and we obtained the higher average ZT value in SnSe_1.05 sample in the range of test temperature.In previous studies on optimizing the properties of SnSe-based thermoelectric materials,we found that the solid solubility of copper,aluminum,zinc,silver and mercury in tin selenide was limited,and the effect of doping was not satisfactory.We have been inspired by metal materials and doped tin selenide with the Devarda’s alloy（aluminum45%,copper 50%,zinc 5%）.The results show that the conductivity of the material is greatly improved,and the power factor of the materials is significantly optimized by doping the Devarda’s alloy.The 0.45（773 K）ZT value was obtained in W_0.005Sn_0.995Se sample,which is almost three times the value of undoped tin selenide.