Research On Thermoelectric Property Of Selenium Components Changed Polycrystaline SnSe

Thermoelectric material is a kind of functional material that can converse the heat energy to electric energy. In today’s energy shot environment, development of new energy materials is of great significance. Researchers also have been looking for materials with high thermoelectric performance for decades.In 2014 an investigation on the thermoelectric performance of single-crystalline SnSe has shown that this material exhibits excellent thermoelectric properties. Since then thermoelectric properties of SnSe have received extensive attention. But considering that single crystal is not suitable for mass production, the complex preparation process and poor mechanical properties, polycrystalline SnSe has thus attracted the attention of researchers. Noenthless, comparied with single crystal SnSe,the thermoelectric properties of polycrystalline SnSe are not so good; the thermoelectric properties need further improvement.In this thesis, firstly, by the method of heating, and high pressure preparing polycrystalline SnSe, the raw materials are put into the vacuum quartz tube for heating, and then use diamond anvil cell to pressure on samples. Polycrystalline SnSe samples show a typical p type semiconductor features, with a low thermal conductivity at the same time. Thermal conductivity increases at first then decreases with the rise of temperature. The max value is 1.61 W/k·m at the temperature of 52.1K. The ZT value increase with the increasing of temperature.Secondly, changing the chemical proportion of Sn and Se when preparing materia, make it deviated from the normal proportion. By adjusting Se excessive and insufficient to adjust the carrier concentration of material, making Sn atoms existing in grain boundary. The results show that when Se excesses, SnSe/SnSe2 composites are obtained, in which the electron concentration increases, and the p type materials are changed into n type. The thermoelectric performance becomes better. For another, we also prepared the polycrystalline SnSe with insufficient Se. The results show that the excessive Sn atoms exist in the grain boundary of the sample, which effects the electrical and thermal transport properties of materials. When Sn excess 1% and 2% in the samples, thermoelectric performance has improved in a certain temperature range compared with the normal proportion SnSe.Finally, polycrystalline SnSe is doped by iodine in the position of Se, the concentration of the electrons increases along with the increase of doping concentration(1%, 2%, 3%). The hole concentration is reduced by doping, leading to the changes in thermoelectric parameters of the sample.Through these studies, the mechanism of thermoelectric polycrystalline SnSe have been understood.It makes sense to further research on SnSe related thermoelectric materials and develope thermoelectric devices.