The Preparation And Research Of Physical Properties Of SnSe Based Anisotropy Thermoelectric Material

The industrialization has made energy consumption more senous in the 21st century,and the erisis of non-renewable energy failure is significant.It is urgent to find new green energy materials.Thermoelectric functional materials can realize the conversion of heat energy and electric energy,and provide the possibility of reuse for the large amount of waste heat loss.SnSe is widely studied as one of thermoelectric materials,and its single crystal thermoelectric value is as high as 2.6,which makes it became one of the high performance thermoelectric materials.However,single crystal is not suitable for mass production,complex preparation and poor mechanical performance.Therefore,the preparation of SnSe polymorphism and improving its thermoelectric properties has become a hot research topic at home and abroad.In this paper,hydrothermal synthesis method is adopted to prepare a multi-crystalline layered SnSe powder with high preferential orientation in a low cost,no additive and simple method.Its preferential orientation is as high as 0.64,and the ratio of peak(400)and peak(111)is 9.85.And two stages of powder growth were proposed.This is the first time to discuss and characterize the optimal orientation of thermoelectric powder materials.The bulks were prepared by plasma discharge sintering using powders synthesized by hydrothermal method and vacuum smelting method,respectively.Then compared thermo electronic performance with those two bulks.The SnSe bulk sample prepared by SPS using the plate-like powders synthesized by hydrothermal reaction shows a stronger orientation,and a special zigzag type texturing feature exists in the entire bulk interior.But the high texturing feature only appears in the surface layer of the SnSe bulk sample prepared by SPS using the irregular powders synthesized by melting reaction.The texture bulk has significant improvement in carrier transport and phonon scattering,with low thermal conductivity and high conductivity,and its highest ZT value is 0.67(2.16 times of the random bulk)in the direction of parallel pressure axis.In order to improve the electric conductivity of polycrystalline SnSe,two kinds of SnSe powders were composited with Au or Cu2-xSe.The SnSe powder prepared by hydrothermal method was comosited with Cu2-xse.The results shows the conductivity improvement is obvious in low temperature zone in the direction of vertical pressure axis for the rich carrier provided by Cu2-xSe.However,due to the scattering effect of rich carrier,its improvement in the high temperature area is not obvious.SnSe is combined with van der Waals force in the direction of parallel pressure axis,which leads to the failure of carrier transport pathway.However,the additional carriers provided by Cu2-xSe under thermal excitation can still improve the conductivity in the middle temperature region in this direction.But due to the significant increase of thermal conductivity,the effect of Cu2-xse composite on thermoelectric performance is not satisfactory.The SnSe powder prepared by smelting method was composited with Au.It was found that the thermoelectric performance of the SnSe/Au bulk was significantly improved along the direction of parallel pressure axis,and its ZT value reached 0.73,which was about 3.6 times higher than that of the pure SnSe sample.The main reason is that Au composite increases the phonon scattering and reduces the thermal conductivity in the direcition of parallel pressure axis.At the same time,the effective conduction path between the layers is constructed by the composite of Au,which significantly improves the conductivity of the SnSe/Au bulk,thus resulting in a great improvement in its thermoelectric properties.