Preparation Of Cu_2-xQ(Q=S,Se) By Solution Method And Study Of Its Thermoelectric Properties

Thermoelectric（ZT）material is a kind of energy conversion material which can convert thermal and electrical energy directly into each other.The thermoelectric devices composed of P/N thermoelectric materials alternately have many advantages such as simple structure,no moving parts,no maintenance,no noise,safety and stability,and have received extensive attention in the 21st century with the world fossil energy crisis.The Cu_2-xQ（Q=S,Se）thermoelectric materials studied in this paper are newtypes of thermoelectric material systems that have developed rapidly in recent years.Compared with the traditional high-performance thermoelectric materials such as antimony telluride and antimony telluride,these materials have the advantages of rich raw materials,low cost,low toxicity and environmental friendliness.And this system material has proposed a new theory of"electron crystal-phononic liquid"by virtue of its superionic phase transition,so that the thermoelectric potential of those materials is very huge.As a new system material,its synthesis process and mechanism need to be clear,the performance of the system material is still relatively low,and the super-ion phase change brings great thermal power advantage,but the material instability caused by long-term copper ion migration is also urgently needed to be solved.This paper focuses on the p-type Cu_2-xQ（Q=S,Se）system thermoelectric materials,using solution method（including hydrothermal method（HS）and wet chemical method（WCM））to prepare compound powder,focuing on the preparation process to determine the synthesis mechanism,control the micro-morphology of the powder,use the spark plasma sintering（SPS）method to prepare polycrystalline bulk materials,optimize the thermoelectric properties of the material through component optimization,and find the solution to the long-term migration of copper ions.The solution to the problem of instability.Studies have shown that the synthesis mechanism of Cu_2-xQ（Q=S,Se）are not the same,and the microstructure of the product can be successfully controlled by adjusting the synthesis process.With the controllability of the microstructure of the solution method,the thermal conductivity of the Cu₂S material was reduced,and the highest ZT value obtained by the sample at 773 K is 0.62（an increase of 26.53%compared with the MA sample prepared by the mechanical alloying（MA）method+SPS）.On this basis,the thermoelectric properties of Cu₂S were successfully improved by powder preparation process improvement and bulk composition control.After the introduction of copper vacancies,the maximum ZT value of the Cu_1.96S bulk sample was 1.01 at 773 K.The P-type Cu₂Se_1.15 polycrystalline bulk was prepared by solution method+SPS.The highest ZT value was 0.75 at 623 K,which is the highest value of Cu-Se system at this temperature.In addition,Cu₂Se_1-xS_x（x=0.1,0.3,0.5）alloy powders were prepared by hydrothermal method combined with the properties of Cu₂S and Cu₂Se.During the early sintering process,the samples spontaneously in-situ phase separation formed a two-phase mixed structure.The phonon scattering is greatly enhanced so that the Cu₂Se_0.9S_0.1 sample achieves a ZT value of up to 1.43 at773 K.In this paper,the long range migration of copper ions and the precipitation of elemental copper are effectively inhibited by means of preparation of composite materials and in-situ formation of the second phase,which provides a new way to solve the problem of electrical and thermal stability of superionic thermoelectric compounds.