Study On The Solution Synthesis And Thermoelectric Properties Of SnSe-based Materials

Thermoelectric materials,which are capable of directly transforming heat into electricity,and vise versa,have a broad application in wasted-heat recovery and refrigeration.Due to the eco-fridenly component elements and high performance,SnSe-based thermoelectric materials have attacted much attention in the field of thermeoelectrics.SnSe polycrystalline materials have relatively lower figure of merit(z T)when compared to its single crystalline counterpart,so it is vitally important to improve the z T of polycrystalline SnSe.Additionally,the high-temperature fabrication of polycrystalline SnSe is time-consuming and energy-intensive,which is an obstacle to its practical application.In this study,bottom-up solution-synthesis methods have been utilized to synthesize SnSe-based thermoelectric materials with tunable compostions and inclusing of reduced graphene oxide(r GO),and detailed exploration of electronic and thermal performance of these materials,building up the foundation for enhancing thermoelectric properties of SnSe-based polycrystalline materials.The main research contents in this study are as follows:(1)SnSe/r GO nanocomposites with tunable r GO weight fractions were prepared in situ by a facile solution method.Detailed characterization results demonstrate the successful reduction and inclusion of graphene oxide(GO)in the composites.The phonon scattering is increased originated from fromed SnSe/r GO interfaces,so that the lattice thermal conductivity is significantly lowered.In addition,the electrical conductivity in the low temperature range is enhanced when appropriate amount of r GO is include into the composites.For example,SnSe/r GO composites with 0.5 wt%exhibits the supreme electrical conductivity of 8000 S m^-1 at 473 K,is above 50%higher than SnSe(3000 S m^-1)and finally the peak power factor of 0.6 m W m^-1 K^-2 is achieved in SnSe/r GO composites with 0.1 wt%.Among all the samples,SnSe/r GO composites with 0.3 wt%obtains the minimum lattice thermal conductivity(?_L)of 0.36W m^-1 K^-1 at 773 K and a maximum z T of 0.91 at 823 K that is 47%higher than SnSe itself.(2)Quaternary Sn S_0.1Se_0.9-xTe_x(x=0.02,0.05,0.08)compounds were fabricated via an multi-step aqueous anion exchange route combined with fast sintering.The electrical conductivity of Sn S_0.1Se_0.88Te_0.02 is significantly enhanced over the Te-free samples over the low temperature range,achieving a peak value of 5760 S m^-1 at 373 K that is increased by 41%compared to the Te-free sample(?4000 S m^-1)and obtaining a maximum power factor of 0.54 m W m^-1 K^-2.The thermoelectric performance of the quaternary samples have been optimized by turning the Te concentration,leading to a highset z T value of 0.43(773 K)in Sn S_0.1Se_0.88Te_0.02.(3)Ternary SnSe_1-xS_x(x=0,0.1,0.2,0.3)micro-plated materials were synthesized utilising a one-pot solvothermal method together with sintering process.Due to the the mass and size differences between S and Se atoms,the lattice thermal conductivity(?_L)of the S-substituted samples in the low temperature range is reduced when compared to the S-free sample.SnSe_0.7S_0.3 obtains a room temperature?_L value of?1.1 W m^-1 K^-1that is?20%lower than SnSe(?_L=1.35 W m^-1 K^-1).Meanwhile,the carrier concentration is enehanced benefitted from S atoms successfully replacement of Se sites and ultimately electraical conductivity is increased.For instance,the room electrical conductivity of SnSe_0.9S_0.1 sample is?4500 S m-1,which is 50%higher than SnSe matrix and peak power factor of 0.58 m W m_-1 k_-2 is obtained.Through tuning the S substitution amount,SnSe_0.9S_0.1 and SnSe_0.8S_0.2 samples obtain the maximum z T of 0.7(773 K),which is 30%higher than SnSe.