Study On The Microstructure And Thermoelectric Properties Of Polycrystalline SnSe Regulated By Magnetic Field

Thermoelectric material which can directly convert thermal energy into electrical energy is expected to solve the energy problem,and it has unique application advantages in power generation and refrigeration.Since the single crystal SnSe realizes the ultrahigh thermoelectric performance of ZT=2.6 in the b-axis direction,SnSe has received extensive attention.In order to achieve a wide range of applications,the optimization of the performance of polycrystalline SnSe has become a research focus.In view of the poor thermoelectric performance of polycrystalline SnSe,a strategy of introducing a magnetic field during hydrothermal synthesis to enhance thermoelectric performance by regulating the microstructure of polycrystalline SnSe,the main research results are as follows:1.Pb-doped polycrystalline SnSe was prepared by strong magnetic field assisted hydrothermal synthesis and spark plasma sintering.It is demonstrated that due to the introduction of the magnetic field,the critical nucleation free energy is reduced and the nucleation rate is increased.Therefore,uniform distribution of Se quantum dots and smaller nanocrystals are formed in the material,which leads to an increase in density of states and an energy filtering effect.The enhancement of the power factor of SnSe is greatly improved,and the maximum power factor of polycrystalline SnSe reaches 5.6μWcm^-1K^-2.In addition,due to the action of nano-precipitation and small-sized grains,the thermal conductivity is significantly reduced,and the lowest thermal conductivity is 0.245 W m^-1K^-1.Benefiting from the enhanced power factor and reduced thermal conductivity,a high figure of merit（ZT）of～2.0 at 873 K.2.Hole doped polycrystalline SnSe were prepared by magnetic field assisted hydrothermal synthesis and spark plasma sintering.It is found that the doping of hole can increase the carrier concentration of SnSe,thereby increasing the conductivity and power factor of polycrystalline SnSe.The magnetic field can regulate the microstructure and improve the energy filtering effect to increase the Seebeck coefficient of SnSe.Furthermore,the thermal conductivity was induced by Pb Se second phase and the smaller grains.finally the hole doped SnSe prepared by magnetic field assisted hydrothermal mathod achieved a high ZT～1.89 duo to its high power factor（PF）and ultralow thermal conductivity.